A Generic Autonomic Signaling Protocol (GRASP)Universität Bremen TZIPostfach 330440D-28359 BremenGermanycabo@tzi.orgDepartment of Computer ScienceUniversity of AucklandPB 92019Auckland1142New Zealandbrian.e.carpenter@gmail.comHuawei Technologies Co., LtdQ14, Huawei CampusNo.156 Beiqing RoadHai-Dian District, Beijing100095P.R. Chinaleo.liubing@huawei.comThis document specifies the GeneRic Autonomic Signaling Protocol (GRASP), which
enables autonomic nodes and autonomic service agents to dynamically discover peers,
to synchronize state with each other, and to negotiate parameter settings with each
other. GRASP depends on an external security environment that is described
elsewhere. The technical objectives and parameters for specific application scenarios
are to be described in separate documents. Appendices briefly discuss requirements
for the protocol and existing protocols with comparable features.The success of the Internet has made IP-based networks bigger and
more complicated. Large-scale ISP and enterprise networks have become more and more
problematic for human based management. Also, operational costs are growing quickly.
Consequently, there are increased requirements for autonomic behavior in the networks.
General aspects of autonomic networks are discussed in
and . One approach is to largely decentralize the logic of network management by migrating it
into network elements. A reference model for autonomic networking on this basis is given in
. The reader should consult this document
to understand how various autonomic components fit together.
In order to fulfill autonomy, devices that embody Autonomic Service Agents
(ASAs, )
have specific signaling requirements. In particular they need to discover each other,
to synchronize state with each other,
and to negotiate parameters and resources directly with each other.
There is no limitation on the types of parameters and resources concerned,
which can include very basic information needed for addressing and routing,
as well as anything else that might be configured in a conventional non-autonomic network.
The atomic unit of discovery, synchronization or negotiation is referred to as a technical
objective, i.e, a configurable parameter or set of parameters
(defined more precisely in ).
Negotiation is an iterative process, requiring multiple message exchanges forming
a closed loop between the negotiating entities. In fact, these entities are
ASAs, normally but not necessarily in different network devices.
State synchronization, when needed,
can be regarded as a special case of negotiation, without iteration.
Both negotiation and synchronization must logically follow discovery.
More details of the requirements are found in .
describes a behavior model for a protocol
intended to support discovery, synchronization and negotiation. The
design of GeneRic Autonomic Signaling Protocol (GRASP) in
of this document is based on this behavior model. The relevant capabilities
of various existing protocols are reviewed in .The proposed discovery mechanism is oriented towards synchronization and
negotiation objectives. It is based on a neighbor discovery process on the
local link, but also supports diversion to peers on other links.
There is no assumption of any particular form of network topology.
When a device starts up with no pre-configuration,
it has no knowledge of the topology. The protocol itself is capable of
being used in a small and/or flat network structure such as a small
office or home network as well as in a large professionally managed network.
Therefore, the discovery mechanism needs to be able to allow a device
to bootstrap itself without making any prior assumptions about network
structure. Because GRASP can be used as part of a decision process among distributed
devices or between networks, it must run in a secure and strongly authenticated
environment.
In realistic deployments, not all devices will
support GRASP. Therefore, some autonomic service agents will directly
manage a group of non-autonomic nodes, and other non-autonomic nodes
will be managed traditionally. Such mixed scenarios
are not discussed in this specification.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
when they appear in ALL CAPS. When these words
are not in ALL CAPS (such as "should" or "Should"), they have their
usual English meanings, and are not to be interpreted as key words.This document uses terminology defined in .The following additional terms are used throughout this document:
Discovery: a process by which an ASA discovers peers
according to a specific discovery objective. The discovery results
may be different according to the different discovery objectives.
The discovered peers may later be used as negotiation
counterparts or as sources of synchronization data. Negotiation: a process by which two ASAs interact
iteratively to agree on parameter settings that best satisfy the
objectives of both ASAs.State Synchronization: a process by which ASAs
interact to receive the current state of parameter
values stored in other ASAs. This is a special case of negotiation
in which information is sent but the ASAs do not request
their peers to change parameter settings. All other definitions
apply to both negotiation and synchronization. Technical Objective (usually abbreviated as Objective):
A technical objective is a data structure, whose main contents
are a name and a value. The value consists of a single configurable
parameter or a set of parameters of some kind. The exact
format of an objective is defined in .
An objective occurs in three contexts: Discovery, Negotiation
and Synchronization. Normally, a given objective will not
occur in negotiation and synchronization contexts simultaneously.
One ASA may support multiple independent objectives.The parameter(s) in the value of a given objective apply to
a specific service or function or action. They may in principle be
anything that can be set to a specific logical, numerical or string
value, or a more complex data structure, by a network node.
Each node is expected to contain one or more ASAs
which may each manage subsidiary non-autonomic nodes.Discovery Objective: an objective in the process of discovery. Its value
may be undefined.Synchronization Objective: an objective whose specific technical content
needs to be synchronized among two or more ASAs. Thus, each ASA will maintain
its own copy of the objective.Negotiation Objective: an objective whose specific technical content
needs to be decided in coordination with another ASA. Again, each ASA will maintain
its own copy of the objective.
A detailed discussion of objectives, including their format, is found in .Discovery Initiator: an ASA that starts discovery
by sending a discovery message referring to a specific discovery
objective.Discovery Responder: a peer that either contains an ASA supporting the discovery objective
indicated by the discovery initiator, or caches the locator(s) of the ASA(s) supporting
the objective. It sends a Discovery Response, as described later.Synchronization Initiator: an ASA that starts synchronization
by sending a request message referring to a specific synchronization
objective.Synchronization Responder: a peer ASA which responds with the
value of a synchronization objective.Negotiation Initiator: an ASA that starts
negotiation by sending a request message referring to a specific
negotiation objective.Negotiation Counterpart: a peer with which the Negotiation
Initiator negotiates a specific negotiation objective.GRASP Instance: This refers to an instantiation of a GRASP protocol engine, likely including
multiple threads or processes as well as dynamic data structures such as a discovery cache, running in
a given security environment on a single device. GRASP Core: This refers to the code and shared data structures of a GRASP instance, which will
communicate with individual ASAs via a suitable Application Programming Interface (API).Interface or GRASP Interface: Unless otherwise stated, these refer to a network
interface - which might be physical or virtual - that a specific instance of
GRASP is currently using. A device might have other interfaces that are not
used by GRASP and which are outside the scope of the autonomic network.A GRASP implementation will be part of the Autonomic Networking Infrastructure (ANI)
in an autonomic node, which must also provide an appropriate security environment.
In accordance with , this SHOULD be the
Autonomic Control Plane (ACP) .
As a result, all autonomic nodes in the ACP are able to trust each other.
It is expected that GRASP will access the ACP by using a typical socket programming interface
and the ACP will make available only network interfaces within the autonomic network.
If there is no ACP, the considerations described in apply.
There will also be one or more Autonomic Service Agents (ASAs). In the minimal case
of a single-purpose device, these components might be fully integrated with GRASP
and the ACP. A more common model is expected to be a multi-purpose device capable of containing
several ASAs, such as a router or large switch. In this case it is expected that the ACP, GRASP and the ASAs will
be implemented as separate processes, which are able to support
asynchronous and simultaneous operations, for example by multi-threading.In some scenarios, a limited negotiation model might be deployed based on a limited
trust relationship such as that between two administrative domains. ASAs might then
exchange limited information and negotiate some particular configurations.GRASP is explicitly designed to operate within a single addressing realm.
Its discovery and flooding mechanisms do not support autonomic operations that
cross any form of address translator or upper layer proxy.A suitable Application Programming Interface (API) will be needed
between GRASP and the ASAs. In some implementations, ASAs would run in user
space with a GRASP library providing the API, and this library would in turn
communicate via system calls with core GRASP functions.
Details of the API are out of scope for the present document.
For further details of possible deployment models, see
.
An instance of GRASP must be aware of the network interfaces it will use, and of the
appropriate global-scope
and link-local addresses. In the presence of the ACP, such information will be available from
the adjacency table discussed in .
In other cases, GRASP must determine such information for itself. Details depend on the
device and operating system. In the rest of this document, the terms 'interfaces'
or 'GRASP interfaces'
refers only to the set of network interfaces that a specific instance
of GRASP is currently using. Because GRASP needs to work with very high reliability, especially during bootstrapping
and during fault conditions, it is essential that every implementation continues to
operate in adverse conditions. For example, discovery failures, or any kind of socket
exception at any time, must not cause irrecoverable failures in GRASP itself, and must
return suitable error codes through the API so that ASAs can also recover.
GRASP must not depend upon non-volatile data storage. All run time error
conditions, and events such as address renumbering, network interface failures,
and CPU sleep/wake cycles, must be handled in such a way that GRASP will still
operate correctly and securely () afterwards.An autonomic node will normally run a single instance of GRASP, used by multiple ASAs.
Possible exceptions are mentioned below.
This section describes the behavior model and general design of
GRASP, supporting discovery, synchronization and negotiation, to
act as a platform for different technical objectives.A generic platform:
The protocol design is generic and independent of the synchronization or
negotiation contents. The technical contents will vary according to the
various technical objectives and the different pairs of
counterparts.Normally, a single main instance of the GRASP protocol engine will exist in an autonomic
node, and each ASA will run as an independent asynchronous process. However, scenarios
where multiple instances of GRASP run in a single node, perhaps with different security
properties, are possible (). In this case, each instance MUST
listen independently for GRASP link-local multicasts,
and all instances MUST be woken by each such multicast, in order for
discovery and flooding to work correctly.
Security infrastructure:
As noted above, the protocol itself has no built-in security functionality,
and relies on a separate secure infrastructure.Discovery, synchronization and negotiation are designed together:
The discovery method and the synchronization and negotiation methods
are designed in the same way and can be combined when this is
useful, allowing a rapid mode of operation described in .
These processes can also be performed independently when appropriate.
Thus, for some objectives, especially those concerned with application layer
services, another discovery mechanism such as the future DNS Service
Discovery MAY be used.
The choice is left to the designers of individual ASAs.A uniform pattern for technical objectives:
The synchronization and negotiation objectives are defined
according to a uniform pattern. The values that they contain
could be carried either in a simple binary format or in a
complex object format. The basic protocol design uses the Concise
Binary Object Representation (CBOR) ,
which is readily extensible for unknown future requirements. A flexible model for synchronization:
GRASP supports synchronization between two nodes, which could be used
repeatedly to perform synchronization among a small number of nodes.
It also supports an unsolicited flooding mode when large groups of nodes,
possibly including all autonomic nodes, need data for the same
technical objective.
There may be some network parameters for which a more traditional flooding
mechanism such as DNCP
is considered more appropriate. GRASP can coexist with DNCP.
A simple initiator/responder model for negotiation:
Multi-party negotiations are very complicated to model and cannot
readily be guaranteed to converge. GRASP uses a simple bilateral model
and can support multi-party negotiations by indirect steps.
Organizing of synchronization or negotiation content:
The technical content transmitted by GRASP will be
organized according to the relevant function or service. The
objectives for different functions or services are kept
separate, because they may be negotiated or synchronized with different
counterparts or have different response times. Thus a normal arrangement
would be a single ASA managing a small set of closely related objectives,
with a version of that ASA in each relevant autonomic node. Further
discussion of this aspect is out of scope for the current document.
Requests and responses in negotiation procedures:
The initiator can negotiate a specific negotiation objective with relevant
counterpart ASAs. It can request relevant information from a counterpart so that it
can coordinate its local configuration. It can request the counterpart to make
a matching configuration. It can request simulation or forecast results by sending
some dry run conditions.
Beyond the traditional yes/no answer, the
responder can reply with a suggested alternative value for the objective
concerned. This would start a bi-directional negotiation
ending in a compromise between the two ASAs.Convergence of negotiation procedures:
To enable convergence, when a responder suggests a new value or
condition in a negotiation step reply, it should be as close as possible
to the original request or previous suggestion. The suggested value of
later negotiation steps should be chosen between the suggested values from
the previous two steps. GRASP provides mechanisms to guarantee convergence
(or failure) in a small number of steps, namely a timeout and a maximum number
of iterations.
Extensibility:
GRASP intentionally does not have a version number, and can be extended by adding new
message types and options. The Invalid Message (M_INVALID) will be used to signal
that an implementation does not recognize a message or option sent by another
implementation. In normal use, new semantics will be added
by defining new synchronization or negotiation objectives.
An instance of GRASP is expected to run as a separate core module,
providing an API (such as ) to interface to
various ASAs.
These ASAs may operate without special privilege, unless they need it for
other reasons (such as configuring IP addresses or manipulating routing
tables).
The GRASP mechanisms used by the ASA are built around GRASP objectives
defined as data structures
containing administrative information such as the objective's unique
name, and its current value. The format and size of the value is
not restricted by the protocol, except that it must be possible to
serialize it for transmission in CBOR, which is no
restriction at all in practice.
GRASP provides the following mechanisms:
A discovery mechanism (M_DISCOVERY, M_RESPONSE), by which an ASA can
discover other ASAs supporting a given objective.
A negotiation request mechanism (M_REQ_NEG), by which an ASA can start
negotiation of an objective with a counterpart ASA. Once a negotiation has
started, the process is symmetrical, and there is a negotiation step message
(M_NEGOTIATE) for each ASA to use in turn. Two other functions support negotiating
steps (M_WAIT, M_END).
A synchronization mechanism (M_REQ_SYN), by which an ASA can request the
current value of an objective from a counterpart ASA. With this,
there is a corresponding response function (M_SYNCH) for an ASA that
wishes to respond to synchronization requests.
A flood mechanism (M_FLOOD), by which an ASA can cause the current value of
an objective to be flooded throughout the autonomic network so that any ASA can
receive it. One application of this is to act as an announcement, avoiding the need for
discovery of a widely applicable objective.Some example messages and simple message flows are provided in .GRASP does not specify transport security because it is meant to be adapted to
different environments. Every solution adopting GRASP MUST specify a security and transport substrate
used by GRASP in that solution.The substrate MUST enforce sending and receiving GRASP messages only between members of a mutually trusted
group running GRASP. Each group member is an instance of GRASP. The group members are nodes of a
connected graph. The group and graph is created by the security and transport substrate and called the GRASP domain.
The substrate must support unicast messages between any group members and (link-local) multicast
messages between adjacent group members. It must deny messages between group members and non group
members. With this model, security is provided by enforcing group membership, but any member of the
trusted group can attack the entire network until revoked. Substrates MUST use cryptographic member authentication and message integrity for GRASP messages.
This can be end-to-end or hop-by-hop across the domain. The security and transport substrate MUST provide mechanisms
to remove untrusted members from the group.If the substrate does not mandate and enforce GRASP message encryption then any service
using GRASP in such a solution MUST provide protection and encryption for message elements whose
exposure could constitute an attack vector.The security and transport substrate for GRASP in the ANI is the ACP. Unless otherwise noted, we assume this
security and transport substrate in the remainder of this document. The ACP does mandate the use of encryption;
therefore GRASP in the ANI can rely on GRASP message being encrypted. The GRASP domain is the ACP: all
nodes in an autonomic domain connected by encrypted virtual links formed by the ACP. The ACP uses
hop-by-hop security (authentication/encryption) of messages. Removal of nodes relies on standard
PKI certificate revocation or expiry of sufficiently short lived certificates. Refer to
for more details.As mentioned in , some GRASP operations might be
performed across an administrative domain boundary by mutual agreement, without the
benefit of an ACP. Such operations
MUST be confined to a separate instance of GRASP with its own copy of all GRASP
data structures running across a separate GRASP domain with a security and transport substrate.
In the most simple case, each point-to-point interdomain GRASP peering could be a
separate domain and the security and transport substrate could be built using transport or network layer
security protocols. This is subject to future specifications. An exception to the requirements for the security and transport substrate exists
for highly constrained subsets of GRASP meant to support the establishment of a security and transport substrate,
described in the following section.Some services may need to use insecure GRASP discovery, response
and flood messages without being able to use pre-existing security associations, for example
as part of discovery for establishing security associations such as a security substrate for
GRASP.Such operations being intrinsically insecure, they need to be confined to link-local
use to minimize the risk of malicious actions. Possible examples
include discovery of candidate ACP neighbors
, discovery of bootstrap
proxies or perhaps
initialization services in networks using GRASP without being fully autonomic
(e.g., no ACP).
Such usage MUST be limited to link-local operations on a single interface and MUST be confined
to a separate insecure instance of GRASP with its own copy of all GRASP
data structures. This instance is nicknamed DULL - Discovery Unsolicited Link-Local.The detailed rules for the DULL instance of GRASP are as follows:
An initiator MAY send Discovery or Flood Synchronization link-local
multicast messages which MUST have a loop count of 1, to prevent
off-link operations.
Other unsolicited GRASP message types MUST NOT be sent.A responder MUST silently discard any message whose loop count is not 1.A responder MUST silently discard any message referring to a GRASP Objective that is
not directly part of a service that requires this insecure mode.A responder MUST NOT relay any multicast messages.A Discovery Response MUST indicate a link-local address.A Discovery Response MUST NOT include a Divert option.A node MUST silently discard any message whose source address is not link-local.To minimize traffic possibly observed by third parties,
GRASP traffic SHOULD be minimized by using only Flood Synchronization
to announce objectives and their associated locators, rather than by using Discovery
and Response. Further details are out of scope for this documentAll GRASP messages, after they are serialized as a CBOR byte string, are transmitted
as such directly over the transport protocol in use. The transport protocol(s) for a GRASP
domain are specified by the security and transport substrate as introduced in .GRASP discovery and flooding messages are designed for GRASP domain wide flooding
through hop-by-hop link-local multicast forwarding between adjacent GRASP nodes. The
GRASP security and transport substrate needs to specify how these link local multicasts
are transported. This can be unreliable transport (UDP) but it SHOULD be reliable
transport (e.g., TCP).If the substrate specifies an unreliable transport such as UDP for discovery and flooding messages,
then it MUST NOT use IP fragmentation because of its loss characteristic, especially
in multi-hop flooding. GRASP MUST then enforce at the user API level a limit to the size
of discovery and flooding messages, so that no fragmentation can occur. For IPv6 transport this
means that those messages must be at most 1280 bytes sized IPv6 packets (unless there is a known
larger minimum link MTU across the whole GRASP domain).All other GRASP messages are unicast beteween group members of the GRASP domain. These
MUST use a reliable transport protocol because GRASP itself does not provide for error detection,
retransmission or flow control. Unless otherwise specified by the security and transport
substrate, TCP MUST be used.The security and transport substrate for GRASP in the ANI is the ACP. Unless otherwise noted,
we assume this security and transport substrate in the remainder of this document when describing
GRASPs message transport. In the ACP, TCP is used for GRASP unicast messages. GRASP discovery and
flooding messages also use TCP: These link-local messages are forwarded by replicating them to
all adjacent GRASP nodes on the link via TCP connections to those adjacent GRASP nodes. Because
of this, GRASP in the ANI has no limitations on the size of discovery and flooding messages with
respect to fragmentation issues. UDP is used in the ANI with GRASP only with DULL when the ACP is built
to discover ACP/GRASP neighbors on links.For link-local UDP multicast, the GRASP protocol listens to the well-known
GRASP Listen Port (). Transport connections for Discovery
and Flooding on relay nodes must terminate in GRASP instances (eg: GRASP ASAs) so
that link-local multicast, hop-by-hop flooding of M_DISCOVERY and M_FLOOD and hop-by-hop forwarding
of M_RESPONSE and caching of those responses along the path work correctly.Unicast transport connections used for synchronization and negotiation can terminate
directly in ASAs that implement objectives and therefore this traffic does not need to
pass through GRASP instances. For this, the ASA listens on its own dynamically assigned ports,
which are communicated to its peers during discovery. Alternatively, the GRASP instance
can also terminate the unicast transport connections and pass the traffic from/to the
ASA if that is preferrable in some implementation (eg: to better decouple ASAs from
network connections).Although discovery and negotiation or synchronization are defined
together in GRASP, they are separate mechanisms. The discovery
process could run independently from the negotiation or synchronization
process. Upon receiving a Discovery ()
message, the
recipient node should return a response message in which it either
indicates itself as a discovery responder or diverts the
initiator towards another more suitable ASA. However, this
response may be delayed if the recipient needs to relay
the discovery onwards, as described below.The discovery action (M_DISCOVERY) will normally be followed by
a negotiation (M_REQ_NEG) or synchronization (M_REQ_SYN) action. The
discovery results could be utilized by the negotiation
protocol to decide which ASA the initiator will negotiate
with.The initiator of a discovery action for a given objective need not
be capable of responding to that objective as a Negotiation Counterpart, as a
Synchronization Responder or as source for flooding. For example, an ASA might perform
discovery even if it only wishes to act a Synchronization Initiator or Negotiation Initiator.
Such an ASA does not itself need to respond to discovery messages.It is also entirely possible to use GRASP discovery without any subsequent
negotiation or synchronization action. In this case, the discovered objective
is simply used as a name during the discovery process and any subsequent
operations between the peers are outside the scope of GRASP.A complete discovery process will start with a multicast (of M_DISCOVERY) on the
local link. On-link neighbors supporting the discovery objective will
respond directly (with M_RESPONSE). A neighbor with multiple interfaces may respond
with a cached discovery response. If it has no cached response, it will relay the
discovery on its other GRASP interfaces. If a node receiving the relayed discovery
supports the discovery objective, it will respond to the relayed discovery.
If it has a cached response, it will respond with that.
If not, it will repeat the discovery process, which thereby becomes iterative.
The loop count and timeout will ensure that the process ends. Further details
are given below.
A Discovery message MAY be sent unicast to a peer node,
which SHOULD then proceed exactly as if the message had been multicast,
except that when TCP is used, the response will be
on the same socket as the query. However,
this mode does not guarantee successful discovery in the general case.
Discovery starts as an on-link operation. The Divert option
can tell the discovery initiator to contact an off-link
ASA for that discovery objective. If the security and transport substrate
of the GRASP domain (see ) uses UDP link-local multicast
then the discovery initiator sends these to the ALL_GRASP_NEIGHBORS link-local
multicast address () and and all GRASP nodes need
to listen to this address to act as discovery responder.
Because this port
is unique in a device, this is a function of the GRASP instance
and not of an individual ASA. As a result, each ASA will need to
register the objectives that it supports with the local GRASP instance.If an ASA in a neighbor device supports the requested discovery objective,
the device SHOULD respond to the link-local multicast with a unicast Discovery Response
message () with locator option(s), unless it is
temporarily unavailable. Otherwise, if the neighbor has cached information
about an ASA that supports the requested discovery objective (usually
because it discovered the same objective before), it SHOULD
respond with a Discovery Response message with a Divert option pointing
to the appropriate Discovery Responder. However, it SHOULD NOT respond
with a cached response on an interface if it learnt that information from
the same interface, because the peer in question will answer directly if still
operational.If a device has no information about the requested discovery objective,
and is not acting as a discovery relay (see below) it MUST silently
discard the Discovery message.The discovery initiator MUST set a reasonable timeout on the
discovery process. A suggested value is 100 milliseconds multiplied by the loop count
embedded in the objective.If no discovery response is received within the timeout,
the Discovery message MAY be repeated, with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions, to limit the load during busy periods. The
details of the backoff algorithm will depend on the use case for the
objective concerned but MUST be consistent with the recommendations
in for low data-volume multicast.
Frequent repetition might be symptomatic of a denial of service attack.After a GRASP device successfully discovers a locator for a Discovery Responder
supporting a specific objective, it SHOULD cache this information, including the interface
index via which it was discovered. This cache record MAY be used for future
negotiation or synchronization, and the locator SHOULD be passed on when appropriate
as a Divert option to another Discovery Initiator.The cache mechanism MUST include a lifetime for each entry. The
lifetime is derived from a time-to-live (ttl) parameter in each
Discovery Response message.
Cached entries MUST be ignored or deleted after their lifetime expires.
In some environments, unplanned address renumbering might occur.
In such cases, the lifetime SHOULD be short compared to
the typical address lifetime. The discovery mechanism
needs to track the node's current address to ensure that Discovery
Responses always indicate the correct address.If multiple Discovery Responders are found for the same objective, they
SHOULD all be cached, unless this creates a resource shortage. The method
of choosing between multiple responders is an implementation choice.
This choice MUST be available to each ASA but the GRASP implementation
SHOULD provide a default choice.Because Discovery Responders will be cached in a finite cache, they might
be deleted at any time. In this case, discovery will need to be repeated. If an
ASA exits for any reason, its locator might still be cached for some time,
and attempts to connect to it will fail. ASAs need to be robust in these
circumstances. A GRASP instance with multiple link-layer interfaces (typically running in a router) MUST
support discovery on all GRASP interfaces. We refer to this as a 'relaying instance'.DULL Instances () are
always single-interface instances and therefore MUST NOT perform discovery relaying.If a relaying instance receives a Discovery message
on a given interface for a specific objective that it does not support and for
which it has not previously cached a Discovery Responder, it MUST relay
the query by re-issuing a new Discovery message as a link-local multicast on its other
GRASP interfaces. The relayed discovery message MUST have the same Session ID and Initiator field
as the incoming (see ). The Initiator IP address field is only
used to allow for disambiguation of the Session ID and is never used to address Response packets.
Response packets are sent back to the relaying instance, not the original initiator.The M_DISCOVERY message does not encode the transport address of the originator or
relay. Response packets must therefore be sent to the transport layer address of the connection
on which the M_DISCOVERY message was received. If the M_DISCOVERY was relayed via a reliable
hop-by-hop transport connection, the response is simply sent back via the same connection.If the M_DISCOVERY was relayed via link-local (eg: UDP) multicast, the response is sent
back via a reliable hop-by-hop transport connection with the same port number as
the source port of the link-local multicast. Therefore, if link-local multicast is
used and M_RESPONSE messages are required (which is the case in almost all GRASP instances
except for the limited use of DULL instances in the ANI), GRASP needs to be able to bind to one
port number on UDP from which to originate the link-local multicast M_DISCOVERY messages
and the same port number on the reliable hop-by-hop transport (eg: TCP by default)
to be able to respond to transport connections from responders that want to send
M_RESPONSE messages back. Note that this port does not need to be the GRASP_LISTEN_PORT.The relaying instance MUST decrement the loop count within the objective, and
MUST NOT relay the Discovery message if the result is zero.
Also, it MUST limit the total rate at which it relays discovery messages
to a reasonable value, in order to mitigate possible denial of service attacks.
For example, the rate limit could be set to a small multiple of the observed
rate of discovery messages during normal operation.
The relaying instance MUST cache the Session ID value and initiator address of each
relayed Discovery message until any Discovery Responses have arrived or
the discovery process has timed out.
To prevent loops, it MUST NOT relay a Discovery message
which carries a given cached Session ID and initiator address more than once.
These precautions avoid discovery loops and mitigate potential overload.Since the relay device is unaware of the timeout set by the original
initiator it SHOULD set a suitable timeout for the relayed discovery.
A suggested value is 100 milliseconds multiplied by the remaining loop count.The discovery results received by the relaying instance MUST in turn be
sent as a Discovery Response message to the Discovery message that caused
the relay action.A Discovery message MAY include an
Objective option. This allows a rapid mode of negotiation
() or
synchronization ().
Rapid mode is currently limited to a single objective
for simplicity of design and implementation. A possible future extension
is to allow multiple objectives in rapid mode for greater efficiency.
A negotiation initiator opens a transport connection to a
counterpart ASA using the address, protocol and port obtained during discovery.
It then sends a negotiation request (using M_REQ_NEG) to the counterpart,
including a specific negotiation objective. It may request the negotiation
counterpart to make a specific configuration. Alternatively, it may
request a certain simulation or forecast result by sending a dry run configuration.
The details, including the distinction between a dry run and a live
configuration change, will be defined separately for each type of negotiation
objective. Any state associated with a dry run operation,
such as temporarily reserving a resource for subsequent use in a live
run, is entirely a matter for the designer of the ASA concerned.Each negotiation session as a whole is subject to a timeout
(default GRASP_DEF_TIMEOUT milliseconds, ),
initialised when the request is sent (see ).
If no reply message of any kind is received within the timeout,
the negotiation request MAY be repeated, with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions. The
details of the backoff algorithm will depend on the use case for the
objective concerned.If the counterpart can immediately apply the requested
configuration, it will give an immediate positive (O_ACCEPT) answer (using M_END).
This will end the negotiation phase immediately. Otherwise, it will
negotiate (using M_NEGOTIATE). It will reply with a proposed alternative configuration
that it can apply (typically, a configuration that uses fewer resources
than requested by the negotiation initiator). This will start a
bi-directional negotiation (using M_NEGOTIATE) to reach a compromise between the two ASAs.The negotiation procedure is ended when one of the negotiation
peers sends a Negotiation Ending (M_END) message, which contains an accept (O_ACCEPT)
or decline (O_DECLINE) option and does not need a response from the negotiation
peer. Negotiation may also end in failure (equivalent to a decline)
if a timeout is exceeded or a loop count is exceeded. When the procedure
ends for whatever reason, the transport connection SHOULD be closed.
A transport session failure is treated as a negotiation failure.A negotiation procedure concerns one objective and one
counterpart. Both the initiator and the counterpart may take part in
simultaneous negotiations with various other ASAs, or in
simultaneous negotiations about different objectives. Thus, GRASP is
expected to be used in a multi-threaded mode or its logical equivalent. Certain negotiation
objectives may have restrictions on multi-threading, for example to
avoid over-allocating resources. Some configuration actions, for example wavelength switching
in optical networks, might take considerable time to execute. The ASA
concerned needs to allow for this by design, but GRASP does allow for
a peer to insert latency in a negotiation process if necessary
(, M_WAIT).A Discovery message MAY include a Negotiation
Objective option. In this case it is as if the initiator sent the sequence
M_DISCOVERY, immediately followed by M_REQ_NEG.
This has implications for the construction of the GRASP core, as it must carefully
pass the contents of the Negotiation Objective option to the ASA so that it
may evaluate the objective directly. When a Negotiation Objective option is
present the ASA replies with an M_NEGOTIATE message (or M_END with O_ACCEPT if it is
immediately satisfied with the proposal), rather than with an M_RESPONSE.
However, if the recipient node does not support rapid mode, discovery will
continue normally.It is possible that a Discovery Response will arrive from a responder that
does not support rapid mode, before such a Negotiation message arrives.
In this case, rapid mode will not occur.This rapid mode could reduce the interactions between
nodes so that a higher efficiency could be achieved. However, a network in which some
nodes support rapid mode and others do not will have complex timing-dependent behaviors.
Therefore, the rapid negotiation function SHOULD be disabled by default.
A synchronization initiator opens a transport connection to a
counterpart ASA using the address, protocol and port obtained during discovery.
It then sends a synchronization request (using M_REQ_SYN) to the
counterpart, including a specific synchronization objective.
The counterpart responds with a Synchronization message (M_SYNCH, )
containing the current value of the requested synchronization
objective. No further messages are needed and the transport
connection SHOULD be closed. A transport session failure is treated
as a synchronization failure.If no reply message of any kind is received within a given timeout
(default GRASP_DEF_TIMEOUT milliseconds, ),
the synchronization request MAY be repeated, with a newly generated
Session ID (). An exponential backoff SHOULD be used
for subsequent repetitions. The
details of the backoff algorithm will depend on the use case for the
objective concerned.In the case just described, the message exchange is unicast and
concerns only one synchronization objective. For large groups of nodes
requiring the same data, synchronization flooding is available. For this,
a flooding initiator MAY send an unsolicited Flood Synchronization message containing
one or more Synchronization Objective option(s), if and only if the specification
of those objectives permits it. This is sent as a multicast message to the
ALL_GRASP_NEIGHBORS multicast address ().Receiving flood multicasts is a function of the GRASP core,
as in the case of discovery multicasts ().To ensure that flooding does not result in a loop, the originator of the Flood Synchronization message
MUST set the loop count in the objectives to a suitable value (the default is GRASP_DEF_LOOPCT).
Also, a suitable mechanism is needed
to avoid excessive multicast traffic. This mechanism MUST be defined as part of the
specification of the synchronization objective(s) concerned. It might be a simple rate
limit or a more complex mechanism such as the Trickle algorithm .A GRASP device with multiple link-layer interfaces (typically a router) MUST
support synchronization flooding on all GRASP interfaces. If it receives a multicast
Flood Synchronization message on a given interface, it MUST relay
it by re-issuing a Flood Synchronization message as a link-local multicast
on its other GRASP interfaces.
The relayed message MUST have the same Session ID as the incoming
message and MUST be tagged with the IP address of its original initiator. Link-layer Flooding is supported by GRASP by setting the loop count to 1,
and sending with a link-local source address. Floods with link-local source addresses
and a loop count other than 1 are invalid, and such messages MUST be discarded.The relaying device MUST decrement the loop count within the first objective, and
MUST NOT relay the Flood Synchronization message if the result is zero.
Also, it MUST limit the total rate at which it relays Flood Synchronization messages
to a reasonable value, in order to mitigate possible denial of service attacks.
For example, the rate limit could be set to a small multiple of the observed
rate of flood messages during normal operation.
The relaying device MUST cache the Session ID value and initiator address of each relayed
Flood Synchronization message for a time not less than twice GRASP_DEF_TIMEOUT milliseconds.
To prevent loops, it MUST NOT relay a Flood Synchronization message
which carries a given cached Session ID and initiator address more than once.
These precautions avoid synchronization loops and mitigate potential overload.Note that this mechanism is unreliable in the case of sleeping nodes,
or new nodes that join the network, or nodes that rejoin the network
after a fault. An ASA that initiates a flood SHOULD repeat the flood
at a suitable frequency, which MUST be consistent with the recommendations
in for low data-volume multicast.
The ASA SHOULD also act as a synchronization responder for
the objective(s) concerned. Thus nodes that require an objective subject to
flooding can either wait for the next flood or request unicast synchronization
for that objective. The multicast messages for synchronization flooding are subject to the security
rules in . In practice this means that they MUST NOT be transmitted
and MUST be ignored on receipt unless there is an operational ACP or equivalent strong
security in place. However, because
of the security weakness of link-local multicast (),
synchronization objectives that are flooded SHOULD NOT contain unencrypted private
information and SHOULD be validated by the recipient ASA.A Discovery message MAY include a Synchronization
Objective option. In this case the Discovery message also acts
as a Request Synchronization message to indicate to the Discovery Responder
that it could directly reply to the Discovery Initiator with
a Synchronization message with synchronization data for rapid processing,
if the discovery target supports the corresponding synchronization
objective. The design implications are similar to those discussed in .It is possible that a Discovery Response will arrive from a responder that
does not support rapid mode, before such a Synchronization message arrives.
In this case, rapid mode will not occur.This rapid mode could reduce the interactions between
nodes so that a higher efficiency could be achieved. However, a network in which some
nodes support rapid mode and others do not will have complex timing-dependent behaviors.
Therefore, the rapid synchronization function SHOULD be configured off by default
and MAY be configured on or off by Intent.ALL_GRASP_NEIGHBORSA link-local
scope multicast address used by a GRASP-enabled device to discover
GRASP-enabled neighbor (i.e., on-link) devices. All devices that
support GRASP are members of this multicast group.IPv6 multicast address: TBD1IPv4 multicast address: TBD2GRASP_LISTEN_PORT (TBD3)A well-known UDP user port that
every GRASP-enabled network device MUST listen to for link-local multicasts when UDP
is used for M_DISCOVERY or M_FLOOD messages in the GRASP instance
This user port MAY also be used to listen for TCP or UDP unicast messages
in a simple implementation of GRASP ().GRASP_DEF_TIMEOUT (60000 milliseconds)The default timeout used to
determine that an operation has failed to complete.GRASP_DEF_LOOPCT (6)The default loop count used to
determine that a negotiation has failed to complete, and to avoid looping messages.GRASP_DEF_MAX_SIZE (2048)The default maximum message size in bytes.This is an up to 32-bit opaque value used to distinguish multiple sessions between
the same two devices. A new Session ID MUST be generated by the initiator for every
new Discovery, Flood Synchronization or Request message. All responses and follow-up messages in the same
discovery, synchronization or negotiation procedure MUST carry the same Session ID.The Session ID SHOULD have a very low collision rate locally. It
MUST be generated by a pseudo-random number generator (PRNG) using a locally
generated seed which is unlikely to be used by any other device in the same
network. The PRNG SHOULD be cryptographically strong .
When allocating a new Session ID, GRASP MUST
check that the value is not already in use and SHOULD check that it has not been
used recently, by consulting a cache of current and recent sessions. In the unlikely
event of a clash, GRASP MUST generate a new value.However, there is a finite probability that two nodes might generate the same
Session ID value. For that reason, when a Session ID is communicated via GRASP, the
receiving node MUST tag it with the initiator's IP address to allow disambiguation.
In the highly unlikely event of two peers opening sessions with the same
Session ID value, this tag will allow the two sessions to be distinguished.
Multicast GRASP messages and their responses, which may be relayed between links,
therefore include a field that carries the initiator's global IP address.There is a highly unlikely race condition in which two peers start simultaneous negotiation
sessions with each other using the same Session ID value. Depending on various
implementation choices, this might lead to the two sessions being confused.
See for details of how to avoid this.This section defines the GRASP message format and message types.
Message types not listed here are reserved for future use. The messages currently defined are:
Discovery and Discovery Response (M_DISCOVERY, M_RESPONSE).Request Negotiation, Negotiation, Confirm Waiting and Negotiation End (M_REQ_NEG, M_NEGOTIATE, M_WAIT, M_END).Request Synchronization, Synchronization, and Flood Synchronization (M_REQ_SYN, M_SYNCH, M_FLOOD.No Operation and Invalid (M_NOOP, M_INVALID).GRASP messages share an identical header format and a
variable format area for options. GRASP message headers and options
are transmitted in Concise Binary Object Representation (CBOR)
. In this specification, they are described
using CBOR data definition language (CDDL)
.
Fragmentary CDDL is used to describe each item in this section. A complete and normative
CDDL specification of GRASP is given in , including constants such
as message types.
Every GRASP message, except the No Operation message, carries a Session ID ().
Options are then presented serially in the options field.In fragmentary CDDL, every GRASP message follows the pattern:The MESSAGE_TYPE indicates the type of the message and thus defines
the expected options. Any options received that are not consistent with
the MESSAGE_TYPE SHOULD be silently discarded. The No Operation (noop) message is described in .The various MESSAGE_TYPE values are defined in .All other message elements are described below and formally defined in .If an unrecognized MESSAGE_TYPE is received in a unicast message,
an Invalid message () MAY be returned. Otherwise the message
MAY be logged and MUST be discarded. If an unrecognized MESSAGE_TYPE is received
in a multicast message, it MAY be logged and MUST be silently discarded.GRASP nodes MUST be able to receive unicast messages of at least GRASP_DEF_MAX_SIZE bytes. GRASP nodes
MUST NOT send unicast messages longer than GRASP_DEF_MAX_SIZE bytes unless a longer size is explicitly
allowed for the objective concerned. For example, GRASP negotiation itself could be used
to agree on a longer message size.The message parser used by GRASP should be configured to know about the GRASP_DEF_MAX_SIZE, or
any larger negotiated message size, so that it may defend against overly long messages.The maximum size of multicast messages (M_DISCOVERY and M_FLOOD) depends on the link
layer technology or link adaptation layer in use.In fragmentary CDDL, a Discovery message follows the pattern:
A discovery initiator sends a Discovery message
to initiate a discovery process for a particular objective option.
The discovery initiator sends all Discovery
messages via UDP to port GRASP_LISTEN_PORT at the link-local
ALL_GRASP_NEIGHBORS multicast address on each link-layer interface in use by GRASP.
It then listens for unicast TCP responses on a given port, and stores the discovery
results (including responding discovery objectives and
corresponding unicast locators).
The listening port used for TCP MUST be the same port as used for sending the
Discovery UDP multicast, on a given interface. In an implementation with a
single GRASP instance in a node this MAY be GRASP_LISTEN_PORT. To support
multiple instances in the same node, the GRASP discovery mechanism in each
instance needs to find, for each interface, a dynamic port that it can bind to
for both sending UDP link-local multicast and listening for TCP, before
initiating any discovery.
The 'initiator' field in the message is a globally unique IP address of the
initiator, for the sole purpose of disambiguating the Session ID
in other nodes. If for some reason the initiator does not
have a globally unique IP address, it MUST use a link-local
address for this purpose that is highly likely to be
unique, for example using . Determination
of a node's globally unique IP address is implementation-dependent.
A Discovery message MUST include exactly one of the following:
a discovery objective option ().
Its loop count MUST be set to a suitable value to prevent discovery
loops (default value is GRASP_DEF_LOOPCT). If the discovery initiator
requires only on-link responses, the loop count MUST be set to 1.
a negotiation objective option (). This
is used both for the purpose of discovery and to indicate
to the discovery target that it MAY directly reply to
the discovery initiatior with a Negotiation message for
rapid processing, if it could act as the corresponding negotiation counterpart.
The sender of such a Discovery message MUST initialize
a negotiation timer and loop count in the same way as a Request Negotiation message
().
a synchronization objective option ().
This is used both for the purpose of discovery and to indicate to the discovery
target that it MAY directly reply to the discovery initiator with a Synchronization message
for rapid processing, if it could act as the corresponding synchronization counterpart.
Its loop count MUST be set to a suitable value to prevent discovery
loops (default value is GRASP_DEF_LOOPCT).As mentioned in , a Discovery message MAY be sent unicast to a peer node,
which SHOULD then proceed exactly as if the message had been multicast.
In fragmentary CDDL, a Discovery Response message follows the pattern:
A node which receives a Discovery message SHOULD send a
Discovery Response message if and only if it can respond to the discovery.
It MUST contain the same Session ID and initiator as the Discovery message.
It MUST contain a time-to-live (ttl) for the validity of the response, given
as a positive integer value in milliseconds. Zero implies a value significantly
greater than GRASP_DEF_TIMEOUT milliseconds (). A suggested
value is ten times that amount.
It MAY include a copy of the discovery objective from
the Discovery message.
It is sent to the sender of the Discovery message via TCP
at the port used to send the Discovery message (as explained in ).
In the case of a relayed Discovery message, the Discovery Response
is thus sent to the relay, not the original initiator.
In all cases, the transport session SHOULD be closed after sending the Discovery Response.
A transport session failure is treated as no response.
If the responding node supports the discovery objective
of the discovery, it MUST include at least one kind of
locator option () to indicate its own
location. A sequence of multiple kinds of locator
options (e.g. IP address option and FQDN option) is also
valid.
If the responding node itself does not support the discovery
objective, but it knows the locator of the discovery
objective, then it SHOULD respond to the discovery message with a
divert option () embedding a locator
option or a combination of multiple kinds of locator
options which indicate the locator(s) of the discovery objective.
More details on the processing of Discovery Responses are given in
.In fragmentary CDDL, Request Negotiation and Request Synchronization messages follow the patterns:
A negotiation or synchronization requesting node
sends the appropriate Request message to the unicast address of the negotiation or
synchronization counterpart, using the appropriate protocol and port numbers
(selected from the discovery result). If the discovery result is an FQDN,
it will be resolved first.A Request message MUST include the relevant objective option. In the case of
Request Negotiation, the objective option MUST include the requested value. When an initiator sends a Request Negotiation message, it MUST initialize a negotiation timer
for the new negotiation thread. The default is GRASP_DEF_TIMEOUT milliseconds. Unless this
timeout is modified by a Confirm Waiting message (),
the initiator will consider that the negotiation has failed when the timer expires. Similarly, when an initiator sends a Request Synchronization, it SHOULD initialize
a synchronization timer. The default is GRASP_DEF_TIMEOUT milliseconds.
The initiator will consider that synchronization has failed
if there is no response before the timer expires.When an initiator sends a Request message, it MUST initialize the loop count
of the objective option with a value defined in the specification of the option
or, if no such value is specified, with GRASP_DEF_LOOPCT. If a node receives a Request message for an objective for which no ASA is currently
listening, it MUST immediately close the relevant socket to indicate this to the initiator.
This is to avoid unnecessary timeouts if, for example, an ASA exits prematurely
but the GRASP core is listening on its behalf.To avoid the highly unlikely race condition in which two nodes simultaneously request
sessions with each other using the same Session ID (), when a node receives a Request message,
it MUST verify that the received Session ID is not already locally active. In case of a clash,
it MUST discard the Request message, in which case the initiator will detect a timeout.In fragmentary CDDL, a Negotiation message follows the pattern:A negotiation counterpart sends a Negotiation
message in response to a Request Negotiation message, a
Negotiation message, or a Discovery message
in Rapid Mode. A negotiation process MAY
include multiple steps.The Negotiation message MUST include the relevant Negotiation Objective option,
with its value updated according to progress in the negotiation. The sender
MUST decrement the loop count by 1. If the loop count becomes zero the message
MUST NOT be sent. In this case the negotiation session has failed and will time out.In fragmentary CDDL, a Negotiation End message follows the pattern:
A negotiation counterpart sends an Negotiation End
message to close the negotiation. It MUST contain
either an accept or a decline option,
defined in and .
It could be sent either by the
requesting node or the responding node.In fragmentary CDDL, a Confirm Waiting message follows the pattern:
A responding node sends a Confirm Waiting message to
ask the requesting node to wait for a further
negotiation response. It might be that the local
process needs more time or that the negotiation
depends on another triggered negotiation. This
message MUST NOT include any other options.
When received, the waiting time value overwrites
and restarts the current negotiation timer
().The responding node SHOULD send a Negotiation, Negotiation End or another
Confirm Waiting message before the negotiation timer expires. If
not, when the initiator's timer expires, the initiator MUST treat
the negotiation procedure as failed.In fragmentary CDDL, a Synchronization message follows the pattern:A node which receives a Request Synchronization, or
a Discovery message in Rapid Mode, sends back a unicast Synchronization
message with the synchronization data, in the form of a GRASP Option for the specific
synchronization objective present in the Request Synchronization.In fragmentary CDDL, a Flood Synchronization message follows the pattern:
A node MAY initiate flooding by sending an unsolicited Flood Synchronization Message
with synchronization data. This MAY be sent to port GRASP_LISTEN_PORT at the
link-local ALL_GRASP_NEIGHBORS multicast address, in accordance
with the rules in .
The initiator address is provided, as described for Discovery messages (),
only to disambiguate the Session ID.
The message MUST contain a time-to-live (ttl) for the validity of the contents, given
as a positive integer value in milliseconds. There is no default;
zero indicates an indefinite lifetime.
The synchronization data are in the form of GRASP Option(s) for specific
synchronization objective(s). The loop count(s) MUST be set to a suitable
value to prevent flood loops (default value is GRASP_DEF_LOOPCT).
Each objective option MAY be followed by a locator option associated with
the flooded objective. In its absence, an empty option MUST be included
to indicate a null locator.
A node that receives a Flood Synchronization message MUST cache the received objectives for
use by local ASAs. Each cached objective MUST be tagged with the locator option sent with it, or with a null
tag if an empty locator option was sent. If a subsequent Flood Synchronization message carrying an objective
with same name and the same tag, the corresponding cached copy of the objective MUST be overwritten.
If a subsequent Flood Synchronization message carrying an objective with same name arrives with a different
tag, a new cached entry MUST be created.Note: the purpose of this mechanism is to allow the recipient of flooded values to distinguish between
different senders of the same objective, and if necessary communicate with them using the locator, protocol
and port included in the locator option. Many objectives will not need this mechanism, so they will be flooded
with a null locator.Cached entries MUST be ignored or deleted after their lifetime expires.In fragmentary CDDL, an Invalid message follows the pattern:
This message MAY be sent by an implementation in response to an incoming unicast message that it considers
invalid. The session-id MUST be copied from the incoming message. The content SHOULD
be diagnostic information such as a partial copy of the invalid message up to the
maximum message size. An M_INVALID message
MAY be silently ignored by a recipient. However, it could be used in support of
extensibility, since it indicates that the remote node does not support a new or
obsolete message or option.An M_INVALID message MUST NOT be sent in response to an M_INVALID message.In fragmentary CDDL, a No Operation message follows the pattern:
This message MAY be sent by an implementation that for practical reasons needs to
initialize a socket. It MUST be silently ignored by a recipient.This section defines the GRASP options for the negotiation
and synchronization protocol signaling. Additional
options may be defined in the future.GRASP options are CBOR objects that MUST start with an unsigned integer identifying
the specific option type carried in this option. These option types are formally
defined in . Apart from that the only format requirement
is that each option MUST be a well-formed CBOR object. In general a CBOR array format
is RECOMMENDED to limit overhead.GRASP options may be defined to include encapsulated GRASP options.The Divert option is used to redirect a GRASP request to another
node, which may be more appropriate for the intended negotiation or synchronization. It
may redirect to an entity that is known as a specific negotiation or synchronization
counterpart (on-link or off-link) or a default gateway. The divert
option MUST only be encapsulated in Discovery Response messages.
If found elsewhere, it SHOULD be silently ignored.A discovery initiator MAY ignore a Divert option if it only requires direct
discovery responses. In fragmentary CDDL, the Divert option follows the pattern:The embedded Locator Option(s) ()
point to diverted destination target(s) in response to a Discovery message. The accept option is used to indicate to the negotiation counterpart
that the proposed negotiation content is accepted.The accept option MUST only be encapsulated in Negotiation End
messages. If found elsewhere, it SHOULD be silently ignored.In fragmentary CDDL, the Accept option follows the pattern:The decline option is used to indicate to the negotiation
counterpart the proposed negotiation content is declined and end the
negotiation process.The decline option MUST only be encapsulated in
Negotiation End messages. If found elsewhere, it SHOULD be
silently ignored.In fragmentary CDDL, the Decline option follows the pattern:Note: there might be scenarios where an ASA wants
to decline the proposed value and restart the negotiation process.
In this case it is an implementation choice whether to send a Decline
option or to continue with a Negotiate message, with an objective
option that contains a null value, or one that contains a new
value that might achieve convergence.These locator options are used to present reachability information for an ASA,
a device or an interface. They are Locator IPv6 Address
Option, Locator IPv4 Address Option, Locator FQDN (Fully
Qualified Domain Name) Option and URI (Uniform Resource Identifier) Option.Since ASAs will normally run as independent user programs, locator options need
to indicate the network layer locator plus the transport protocol and port number for
reaching the target. For this reason, the Locator Options for IP addresses
and FQDNs include this information explicitly. In the case of the URI Option,
this information can be encoded in the URI itself.Note: It is assumed that all locators used in locator options are in scope throughout
the GRASP domain. As stated in ,
GRASP is not intended to work across disjoint addressing
or naming realms. In fragmentary CDDL, the IPv6 address option follows the pattern:The content of this option is a binary IPv6 address followed by the protocol number and port number to be used.Note 1: The IPv6 address MUST normally have global scope. However, during initialization,
a link-local address MAY be used for specific objectives only (). In this case
the corresponding Discovery Response message MUST be sent via the interface to which the link-local
address applies.Note 2: A link-local IPv6 address MUST NOT be used when this option is included in a Divert option.Note 3: The IPPROTO values are taken from the existing IANA Protocol Numbers registry in order
to specify TCP or UDP. If GRASP
requires future values that are not in that registry, a new registry for values outside the range 0..255
will be needed.In fragmentary CDDL, the IPv4 address option follows the pattern:The content of this option is a binary IPv4 address followed by the protocol number and port number to be used.Note: If an operator has internal network address translation for IPv4,
this option MUST NOT be used within the Divert option.In fragmentary CDDL, the FQDN option follows the pattern:The content of this option is the Fully Qualified Domain Name of the target followed by the protocol number and port number to be used.
Note 1: Any FQDN which might not be valid throughout the network in question,
such as a Multicast DNS name , MUST NOT be used when
this option is used within the Divert option.Note 2: Normal GRASP operations are not expected to use this option. It is intended for
special purposes such as discovering external services.In fragmentary CDDL, the URI option follows the pattern:The content of this option is the Uniform Resource Identifier of the target
followed by the protocol number and port number to be used (or by null values if not required)
.
Note 1: Any URI which might not be valid throughout the network in question,
such as one based on a Multicast DNS name , MUST NOT be used when
this option is used within the Divert option.Note 2: Normal GRASP operations are not expected to use this option. It is intended for
special purposes such as discovering external services. Therefore its use is not further
described in this specification.An objective option is used to identify objectives for
the purposes of discovery, negotiation or synchronization.
All objectives MUST be in the following format,
described in fragmentary CDDL:All objectives are identified by a unique name which is a UTF-8 string , to be
compared byte by byte. The names of generic objectives MUST NOT include a colon (":")
and MUST be registered with IANA ().The names of privately defined objectives MUST include at least one colon (":").
The string preceding the last colon in the name MUST be globally unique and in some
way identify the entity or person defining the objective. The following three methods
MAY be used to create such a globally unique string:
The unique string is a decimal number representing a registered 32 bit Private Enterprise
Number (PEN) that uniquely identifies the enterprise
defining the objective.The unique string is a fully qualified domain name that uniquely identifies the entity or person
defining the objective.The unique string is an email address that uniquely identifies the entity or person
defining the objective.
The GRASP protocol treats the objective name as an opaque string. For example, "EX1", "32473:EX1",
"example.com:EX1", "example.org:EX1 and "user@example.org:EX1" would be five different objectives.The 'objective-flags' field is described below.The 'loop-count' field is used for terminating negotiation as described in
. It is also used for terminating discovery as
described in , and for terminating flooding as described in
. It is placed in the objective rather than in the GRASP
message format because, as far as the ASA is concerned, it is a property of the
objective itself.
The 'objective-value' field is to express the actual value of a negotiation
or synchronization objective. Its format is defined in the
specification of the objective and may be a simple value
or a data structure of any kind, as long as it can be represented in CBOR.
It is optional because it is optional in a Discovery or Discovery Response message.An objective may be relevant for discovery only, for discovery and negotiation, or
for discovery and synchronization. This is expressed in the objective by logical flag bits:These bits are independent and may be combined appropriately, e.g. (F_DISC and F_SYNCH) or
(F_DISC and F_NEG) or (F_DISC and F_NEG and F_NEG_DRY).Note that for a given negotiation session, an objective must be either used for negotiation, or for
dry-run negotiation. Mixing the two modes in a single negotiation is not possible.As mentioned above, Objective Options MUST be assigned a unique name.
As long as privately defined Objective Options obey the rules above, this document
does not restrict their choice of name, but the entity or person concerned SHOULD publish the names in use. Names are expressed as UTF-8 strings for convenience in designing Objective Options for
localized use. For generic usage, names expressed in the ASCII subset of UTF-8 are RECOMMENDED.
Designers planning to use non-ASCII names are strongly advised to consult
or its successor
to understand the complexities involved. Since the GRASP protocol compares names byte by byte,
all issues of Unicode profiling and canonicalization MUST be specified in the design of the
Objective Option.All Objective Options MUST respect the CBOR patterns defined above as "objective"
and MUST replace the "any" field with a valid CBOR data definition
for the relevant use case and application. An Objective Option that contains no additional
fields beyond its "loop-count" can only be a discovery objective and MUST only be used
in Discovery and Discovery Response messages.The Negotiation Objective Options contain negotiation objectives,
which vary according to different functions/services. They MUST
be carried by Discovery, Request Negotiation or Negotiation messages only. The negotiation
initiator MUST set the initial "loop-count" to a value specified in the
specification of the objective or, if no such value is specified, to
GRASP_DEF_LOOPCT.For most scenarios, there should be initial values in the
negotiation requests. Consequently, the Negotiation Objective options MUST
always be completely presented in a Request Negotiation message, or in a Discovery
message in rapid mode. If there is no
initial value, the value field SHOULD be set to the 'null' value defined
by CBOR.Synchronization Objective Options are similar, but MUST be carried
by Discovery, Discovery Response, Request Synchronization, or Flood Synchronization
messages only. They include
value fields only in Synchronization or Flood Synchronization messages. The design of an objective interacts in various ways with the design of the ASAs
that will use it. ASA design considerations are discussed in
.Generic objective options MUST be specified in documents
available to the public and SHOULD be designed to use either
the negotiation or the synchronization mechanism described above.
As noted earlier, one negotiation objective is handled by each
GRASP negotiation thread. Therefore, a negotiation objective, which is
based on a specific function or action, SHOULD be organized as a single
GRASP option. It is NOT RECOMMENDED to organize multiple negotiation
objectives into a single option, nor to split a single function
or action into multiple negotiation objectives. It is important to understand that GRASP negotiation does not
support transactional integrity. If transactional integrity is needed for
a specific objective, this must be ensured by the ASA. For example, an ASA
might need to ensure that it only participates in one negotiation thread
at the same time. Such an ASA would need to stop listening for incoming
negotiation requests before generating an outgoing negotiation request.A synchronization objective SHOULD be organized as a single GRASP option.Some objectives will support more than one operational mode.
An example is a negotiation objective with both a "dry run" mode
(where the negotiation is to find out whether the other end can in fact
make the requested change without problems) and a "live" mode, as explained
in . The semantics of such
modes will be defined in the specification of the objectives. These
objectives SHOULD include flags indicating the
applicable mode(s).An issue requiring particular attention is that GRASP itself is
not a transactionally safe protocol. Any state associated with a dry run operation,
such as temporarily reserving a resource for subsequent use in a live
run, is entirely a matter for the designer of the ASA concerned.As indicated in , an objective's value may
include multiple parameters. Parameters
might be categorized into two classes: the obligatory ones presented as
fixed fields; and the optional ones presented in
some other form of data structure embedded in CBOR. The format might be
inherited from an existing management or configuration protocol, with
the objective option acting as a carrier for that format.
The data structure might be defined in a formal language, but that is a
matter for the specifications of individual objectives.
There are many candidates, according to the context, such as ABNF, RBNF,
XML Schema, YANG, etc. The GRASP protocol itself is agnostic on
these questions. The only restriction is that the format can be mapped
into CBOR.It is NOT RECOMMENDED to mix parameters that have significantly
different response time characteristics in a single objective. Separate
objectives are more suitable for such a scenario.All objectives MUST support GRASP discovery. However, as mentioned
in , it is acceptable for an ASA to use an alternative method
of discovery. Normally, a GRASP objective will refer to specific technical parameters
as explained in . However, it is acceptable to define
an abstract objective for the purpose of managing or coordinating ASAs.
It is also acceptable to define a special-purpose objective for purposes
such as trust bootstrapping or formation of the ACP.
To guarantee convergence, a limited number of rounds or a timeout is needed
for each negotiation objective.
Therefore, the definition of each negotiation objective SHOULD clearly specify
this, for example a default loop count and timeout,
so that the negotiation can always be terminated properly. If not,
the GRASP defaults will apply.
There must be a well-defined procedure for concluding that a negotiation cannot
succeed, and if so deciding what happens next (e.g., deadlock
resolution, tie-breaking, or revert to best-effort
service). This MUST be specified for individual negotiation objectives.
The names "EX0" through "EX9" have been reserved for experimental options.
Multiple names have been assigned because a single experiment
may use multiple options simultaneously. These experimental options
are highly likely to have different meanings when used for different
experiments. Therefore, they SHOULD NOT be used without an explicit
human decision and MUST NOT be used in unmanaged networks such as
home networks.These names are also RECOMMENDED for use in documentation
examples.Two prototype implementations of GRASP have been made.Name: BaseNegotiator.cpp, msg.cpp, Client.cpp, Server.cppDescription: C++ implementation of GRASP core and APIMaturity: Prototype code, interoperable between Ubuntu.Coverage: Corresponds to draft-carpenter-anima-gdn-protocol-03. Since it was implemented
based on the old version draft, the most significant limitations comparing to current protocol design
include:
Not support CBORNot support FloodingNot support loop avoidanceonly coded for IPv6, any IPv4 is accidentalLicensing: Huawei License.Experience: https://github.com/liubingpang/IETF-Anima-Signaling-Protocol/blob/master/README.mdContact: https://github.com/liubingpang/IETF-Anima-Signaling-ProtocolName: graspyDescription: Python 3 implementation of GRASP core and API.Maturity: Prototype code, interoperable between Windows 7 and Linux.Coverage: Corresponds to draft-ietf-anima-grasp-13. Limitations include:
insecure: uses a dummy ACP moduleonly coded for IPv6, any IPv4 is accidentalFQDN and URI locators incompletely supportedno code for rapid moderelay code is lazy (no rate control)all unicast transactions use TCP (no unicast UDP). Experimental code for unicast UDP proved to be complex and brittle.optional Objective option in Response messages not implementedworkarounds for defects in Python socket module and Windows socket peculiaritiesLicensing: Simplified BSDExperience: Tested on Windows, Linux and MacOS. https://www.cs.auckland.ac.nz/~brian/graspy/graspy.pdfContact: https://www.cs.auckland.ac.nz/~brian/graspy/A successful attack on negotiation-enabled nodes
would be extremely harmful, as such nodes might end up with a completely
undesirable configuration that would also adversely affect their peers.
GRASP nodes and messages therefore require full protection.
As explained in , GRASP MUST run within a secure
environment such as the Autonomic Control Plane
,
except for the constrained instances described in .- AuthenticationA cryptographically authenticated identity for each device is
needed in an autonomic network. It is not safe to assume that a
large network is physically secured against interference or that all
personnel are trustworthy. Each autonomic node MUST be capable
of proving its identity and authenticating its messages. GRASP
relies on a separate external certificate-based security mechanism to support
authentication, data integrity protection, and anti-replay protection.Since GRASP must be deployed in an existing secure environment,
the protocol itself specifies nothing concerning the trust anchor and
certification authority. For example, in the Autonomic Control Plane
, all nodes can
trust each other and the ASAs installed in them.If GRASP is used temporarily without an external security mechanism,
for example during system bootstrap (),
the Session ID () will act as a nonce to
provide limited protection against third parties injecting responses.
A full analysis of the secure bootstrap process is in
. - Authorization and RolesThe GRASP protocol is agnostic about the roles and capabilities of individual
ASAs and about which objectives a particular ASA is authorized to support. An implementation
might support precautions such as allowing only one ASA in a given node to modify
a given objective, but this may not be appropriate in all cases. For example,
it might be operationally useful to allow an old and a new version of the same
ASA to run simultaneously during an overlap period. These questions are out
of scope for the present specification.- Privacy and confidentialityGRASP is intended for network management purposes involving
network elements, not end hosts. Therefore, no personal information
is expected to be involved in the signaling protocol, so there should be no direct
impact on personal privacy. Nevertheless, applications that do
convey personal information cannot be excluded. Also, traffic flow paths, VPNs,
etc. could be negotiated, which could be of interest for traffic
analysis. Operators generally want to conceal details of their
network topology and traffic density from outsiders. Therefore,
since insider attacks cannot be excluded in a large
network, the security mechanism for the protocol MUST
provide message confidentiality. This is why
requires either an ACP or an alternative security mechanism.- Link-local multicast securityGRASP has no reasonable alternative to using link-local multicast
for Discovery or Flood Synchronization messages and these messages are sent in clear and
with no authentication. They are only sent on interfaces within the autonomic network
(see and ).
They are however available to on-link eavesdroppers, and
could be forged by on-link attackers. In the case of Discovery, the Discovery Responses
are unicast and will therefore be protected (), and an untrusted
forger will not be able to receive responses. In the case of Flood Synchronization, an on-link
eavesdropper will be able to receive the flooded objectives but there is no response
message to consider. Some precautions for Flood Synchronization messages
are suggested in .- DoS Attack ProtectionGRASP discovery partly relies on insecure link-local multicast. Since
routers participating in GRASP sometimes relay discovery messages from one link
to another, this could be a vector for denial of service attacks. Some
mitigations are specified in . However, malicious
code installed inside the Autonomic Control Plane could always launch
DoS attacks consisting of spurious discovery messages, or of spurious
discovery responses. It is important that firewalls prevent any GRASP messages
from entering the domain from an unknown source. - Security during bootstrap and discoveryA node cannot trust GRASP traffic from other nodes until the security
environment (such as the ACP) has identified the trust anchor and can authenticate traffic
by validating certificates for other nodes. Also, until it has succesfully enrolled
a node cannot
assume that other nodes are able to authenticate its own traffic.
Therefore, GRASP discovery during the bootstrap phase for a new device
will inevitably be insecure. Secure synchronization and negotiation
will be impossible until enrollment is complete. Further details
are given in .- Security of discovered locatorsWhen GRASP discovery returns an IP address, it MUST be that of a node
within the secure environment (). If it returns
an FQDN or a URI, the ASA that receives it MUST NOT assume that the
target of the locator is within the secure environment.
grasp-message = (message .within message-structure) / noop-message
message-structure = [MESSAGE_TYPE, session-id, ?initiator,
*grasp-option]
MESSAGE_TYPE = 0..255
session-id = 0..4294967295 ;up to 32 bits
grasp-option = any
message /= discovery-message
discovery-message = [M_DISCOVERY, session-id, initiator, objective]
message /= response-message ;response to Discovery
response-message = [M_RESPONSE, session-id, initiator, ttl,
(+locator-option // divert-option), ?objective]
message /= synch-message ;response to Synchronization request
synch-message = [M_SYNCH, session-id, objective]
message /= flood-message
flood-message = [M_FLOOD, session-id, initiator, ttl,
+[objective, (locator-option / [])]]
message /= request-negotiation-message
request-negotiation-message = [M_REQ_NEG, session-id, objective]
message /= request-synchronization-message
request-synchronization-message = [M_REQ_SYN, session-id, objective]
message /= negotiation-message
negotiation-message = [M_NEGOTIATE, session-id, objective]
message /= end-message
end-message = [M_END, session-id, accept-option / decline-option ]
message /= wait-message
wait-message = [M_WAIT, session-id, waiting-time]
message /= invalid-message
invalid-message = [M_INVALID, session-id, ?any]
noop-message = [M_NOOP]
divert-option = [O_DIVERT, +locator-option]
accept-option = [O_ACCEPT]
decline-option = [O_DECLINE, ?reason]
reason = text ;optional UTF-8 error message
waiting-time = 0..4294967295 ; in milliseconds
ttl = 0..4294967295 ; in milliseconds
locator-option /= [O_IPv4_LOCATOR, ipv4-address,
transport-proto, port-number]
ipv4-address = bytes .size 4
locator-option /= [O_IPv6_LOCATOR, ipv6-address,
transport-proto, port-number]
ipv6-address = bytes .size 16
locator-option /= [O_FQDN_LOCATOR, text, transport-proto, port-number]
locator-option /= [O_URI_LOCATOR, text,
transport-proto / null, port-number / null]
transport-proto = IPPROTO_TCP / IPPROTO_UDP
IPPROTO_TCP = 6
IPPROTO_UDP = 17
port-number = 0..65535
initiator = ipv4-address / ipv6-address
objective-flags = uint .bits objective-flag
objective-flag = &(
F_DISC: 0 ; valid for discovery
F_NEG: 1 ; valid for negotiation
F_SYNCH: 2 ; valid for synchronization
F_NEG_DRY: 3 ; negotiation is dry-run
)
objective = [objective-name, objective-flags, loop-count, ?objective-value]
objective-name = text ;see section "Format of Objective Options"
objective-value = any
loop-count = 0..255
; Constants for message types and option types
M_NOOP = 0
M_DISCOVERY = 1
M_RESPONSE = 2
M_REQ_NEG = 3
M_REQ_SYN = 4
M_NEGOTIATE = 5
M_END = 6
M_WAIT = 7
M_SYNCH = 8
M_FLOOD = 9
M_INVALID = 99
O_DIVERT = 100
O_ACCEPT = 101
O_DECLINE = 102
O_IPv6_LOCATOR = 103
O_IPv4_LOCATOR = 104
O_FQDN_LOCATOR = 105
O_URI_LOCATOR = 106
]]>This document defines the GeneRic Autonomic Signaling Protocol (GRASP). explains the following link-local multicast
addresses, which IANA is requested to assign for use by GRASP:(IPv6): (TBD1).
Assigned in the IPv6 Link-Local Scope Multicast Addresses registry.(IPv4): (TBD2).
Assigned in the IPv4 Multicast Local Network Control Block.
explains the following User Port,
which IANA is requested to assign for use by GRASP for both UDP and TCP:GRASP_LISTEN_PORT: (TBD3)
Service Name: Generic Autonomic Signaling Protocol (GRASP)
Transport Protocols: UDP, TCP
Assignee: iesg@ietf.org
Contact: chair@ietf.org
Description: See
Reference: RFC XXXX (this document)The IANA is requested to create a GRASP Parameter Registry
including two registry tables. These are the GRASP Messages and Options Table and
the GRASP Objective Names Table.GRASP Messages and Options Table. The values in this table are names paired with decimal
integers. Future values MUST be assigned using the Standards Action policy
defined by . The following initial values are assigned by this document:GRASP Objective Names Table. The values in this table are UTF-8 strings which
MUST NOT include a colon (":"), according to .
Future values MUST be assigned using the Specification Required policy
defined by .To assist expert review of a new objective, the specification should include
a precise description of the format of the new objective, with sufficient explanation
of its semantics to allow independent implementations. See for
more details. If the new objective is similar in name or purpose to a previously
registered objective, the specification should explain why a new objective is justified. The following initial values are assigned by this document:A major contribution to the original version of this document was made by Sheng Jiang
and significant contributions were made by Toerless Eckert.
Significant early review inputs were received from Joel Halpern, Barry Leiba,
Charles E. Perkins, and Michael Richardson. William Atwood provided important assistance in
debugging a prototype implementation.Valuable comments were received from
Michael Behringer,
Jeferson Campos Nobre,
Laurent Ciavaglia,
Zongpeng Du,
Yu Fu,
Joel Jaeggli,
Zhenbin Li,
Dimitri Papadimitriou,
Pierre Peloso,
Reshad Rahman,
Markus Stenberg,
Martin Stiemerling,
Rene Struik,
Martin Thomson,
Dacheng Zhang,
and participants in the NMRG research group,
the ANIMA working group,
and the IESG.68. (Placeholder)1. UDP vs TCP: For now, this specification suggests UDP and TCP as
message transport mechanisms. This is not clarified yet. UDP
is good for short conversations, is necessary for multicast discovery,
and generally fits the discovery and divert scenarios
well. However, it will cause problems with large messages. TCP is good
for stable and long sessions, with a little bit of time
consumption during the session establishment stage. If messages
exceed a reasonable MTU, a TCP mode will be required in any case.
This question may be affected by the security discussion.
RESOLVED by specifying UDP for short message and TCP for longer one.
2. DTLS or TLS vs built-in security mechanism. For now, this
specification has chosen a PKI based built-in security mechanism
based on asymmetric cryptography. However, (D)TLS might be chosen as security solution
to avoid duplication of effort. It also allows essentially similar security for short
messages over UDP and longer ones over TCP. The implementation trade-offs are different.
The current approach requires expensive asymmetric cryptographic calculations
for every message. (D)TLS has startup overheads but cheaper crypto per message.
DTLS is less mature than TLS.
RESOLVED by specifying external security (ACP or (D)TLS).
The following open issues applied only if the original security model was retained:
2.1. For replay protection, GRASP currently requires every participant to have an
NTP-synchronized clock. Is this OK for low-end devices, and how does
it work during device bootstrapping?
We could take the Timestamp out of signature option, to become
an independent and OPTIONAL (or RECOMMENDED) option.2.2. The Signature Option states that this option
could be any place in a message. Wouldn't it be better to specify a position
(such as the end)? That would be much simpler to implement. RESOLVED by changing security model.3. DoS Attack Protection needs work.
RESOLVED by adding text.4. Should we consider preferring a text-based approach to
discovery (after the initial discovery needed for bootstrapping)?
This could be a complementary mechanism for multicast based discovery, especially
for a very large autonomic network. Centralized registration could be automatically
deployed incrementally. At the very first stage, the repository could be empty;
then it could be filled in by the objectives discovered by different devices (for example
using Dynamic DNS Update). The more records are stored in the repository, the less the
multicast-based discovery is needed. However, if we adopt such a mechanism, there would be
challenges: stateful solution, and security.
RESOLVED for now by adding optional use of DNS-SD by ASAs. Subsequently removed
by editors as irrelevant to GRASP istelf.
5. Need to expand description of the minimum requirements for
the specification of an individual discovery, synchronization or
negotiation objective.
RESOLVED for now by extra wording.6. Use case and protocol walkthrough. A description of how a node starts up,
performs discovery, and conducts negotiation and synchronisation for a sample
use case would help readers to understand the applicability of this specification.
Maybe it should be an artificial use case or maybe a simple real one, based on
a conceptual API. However, the authors have not yet decided whether to have a
separate document or have it in the protocol document.
RESOLVED: recommend a separate document.7. Cross-check against other ANIMA WG documents for consistency and gaps.
RESOLVED: Satisfied by WGLC.8. Consideration of ADNCP proposal.
RESOLVED by adding optional use of DNCP for flooding-type synchronization.9. Clarify how a GDNP instance knows whether it is running inside the ACP. (Sheng)
RESOLVED by improved text.10. Clarify how a non-ACP GDNP instance initiates (D)TLS. (Sheng)
RESOLVED by improved text and declaring DTLS out of scope for this draft.
11. Clarify how UDP/TCP choice is made. (Sheng) [Like DNS? - Brian]
RESOLVED by improved text.12. Justify that IP address within ACP or (D)TLS environment is sufficient to
prove AN identity; or explain how Device Identity Option is used. (Sheng)
RESOLVED for now: we assume that all ASAs in a device are trusted
as soon as the device is trusted, so they share credentials. In that case
the Device Identity Option is useless. This needs to be reviewed later.13. Emphasise that negotiation/synchronization are independent from discovery,
although the rapid discovery mode includes the first step of a negotiation/synchronization.
(Sheng)
RESOLVED by improved text. 14. Do we need an unsolicited flooding mechanism for discovery (for discovery results
that everyone needs), to reduce scaling impact of flooding discovery messages? (Toerless)
RESOLVED: Yes, added to requirements and solution. 15. Do we need flag bits in Objective Options to distinguish distinguish Synchronization
and Negotiation "Request" or rapid mode "Discovery" messages? (Bing)
RESOLVED: yes, work on the API showed that these flags are essential. 16. (Related to issue 14). Should we revive the "unsolicited Response" for flooding
synchronisation data? This has to be done carefully due to the well-known issues with
flooding, but it could be useful, e.g. for Intent distribution, where DNCP doesn't
seem applicable.
RESOLVED: Yes, see #14.
17. Ensure that the discovery mechanism is completely proof against loops
and protected against duplicate responses.
RESOLVED: Added loop count mechanism.
18. Discuss the handling of multiple valid discovery responses.
RESOLVED: Stated that the choice must be available to the ASA
but GRASP implementation should pick a default. 19. Should we use a text-oriented format such as JSON/CBOR instead of
native binary TLV format?
RESOLVED: Yes, changed to CBOR. 20. Is the Divert option needed? If a discovery response provides a valid
IP address or FQDN, the recipient doesn't gain any extra knowledge from the Divert.
On the other hand, the presence of Divert informs the receiver that the target
is off-link, which might be useful sometimes.
RESOLVED: Decided to keep Divert option. 21. Rename the protocol as GRASP (GeneRic Autonomic Signaling Protocol)?
RESOLVED: Yes, name changed.22. Does discovery mechanism scale robustly as needed? Need hop limit on relaying?
RESOLVED: Added hop limit.23. Need more details on TTL for caching discovery responses.
RESOLVED: Done.24. Do we need "fast withdrawal" of discovery responses?
RESOLVED: This doesn't seem necessary. If an ASA exits or stops supporting a given objective,
peers will fail to start future sessions and will simply repeat discovery. 25. Does GDNP discovery meet the needs of multi-hop DNS-SD?
RESOLVED: Decided not to consider this further as a GRASP protocol issue. GRASP objectives
could embed DNS-SD formats if needed.26. Add a URL type to the locator options (for security bootstrap etc.)
RESOLVED: Done, later renamed as URI. 27. Security of Flood multicasts ().
RESOLVED: added text.28. Does ACP support secure link-local multicast?
RESOLVED by new text in the Security Considerations.29. PEN is used to distinguish vendor options. Would it be better to use
a domain name? Anything unique will do.
RESOLVED: Simplified this by removing PEN field and changing naming rules
for objectives.30. Does response to discovery require randomized delays to mitigate amplification attacks?
RESOLVED: WG feedback is that it's unnecessary.31. We have specified repeats for failed discovery etc. Is that sufficient to deal with sleeping nodes?
RESOLVED: WG feedback is that it's unnecessary to say more.32. We have one-to-one synchronization and flooding synchronization. Do we also need
selective flooding to a subset of nodes?
RESOLVED: This will be discussed as a protocol extension in a separate draft
(draft-liu-anima-grasp-distribution).33. Clarify if/when discovery needs to be repeated.
RESOLVED: Done.34. Clarify what is mandatory for running in ACP, expand discussion of security boundary
when running with no ACP - might rely on the local PKI infrastructure.
RESOLVED: Done.35. State that role-based authorization of ASAs is out of scope for GRASP.
GRASP doesn't recognize/handle any "roles".
RESOLVED: Done.36. Reconsider CBOR definition for PEN syntax.
( objective-name = text / [pen, text] ; pen = uint )
RESOLVED: See issue 29.37. Are URI locators really needed?
RESOLVED: Yes, e.g. for security bootstrap discovery, but added note that
addresses are the normal case (same for FQDN locators).38. Is Session ID sufficient to identify relayed responses?
Isn't the originator's address needed too?
RESOLVED: Yes, this is needed for multicast messages and their responses.39. Clarify that a node will contain one GRASP instance supporting multiple ASAs.
RESOLVED: Done.40. Add a "reason" code to the DECLINE option?
RESOLVED: Done.41. What happens if an ASA cannot conveniently use one of the GRASP mechanisms?
Do we (a) add a message type to GRASP, or (b) simply pass the discovery results to the ASA so
that it can open its own socket?
RESOLVED: Both would be possible, but (b) is preferred.42. Do we need a feature whereby an ASA can bypass the ACP and use the data plane
for efficiency/throughput? This would require discovery to return non-ACP addresses
and would evade ACP security.
RESOLVED: This is considered out of scope for GRASP, but a comment has been added
in security considerations. 43. Rapid mode synchronization and negotiation is currently limited to
a single objective for simplicity of design and implementation. A future
consideration is to allow multiple objectives in rapid mode for greater efficiency.
RESOLVED: This is considered out of scope for this version.44. In requirement T9, the words that encryption "may not be required in all deployments"
were removed. Is that OK?.
RESOLVED: No objections.45. Device Identity Option is unused. Can we remove it completely?.
RESOLVED: No objections. Done.46. The 'initiator' field in DISCOVER, RESPONSE and FLOOD messages is intended to assist
in loop prevention. However, we also have the loop count for that. Also, if we create a new
Session ID each time a DISCOVER or FLOOD is relayed, that ID can be disambiguated
by recipients. It would be simpler to remove the initiator from the messages, making
parsing more uniform. Is that OK?
RESOLVED: Yes. Done.47. REQUEST is a dual purpose message (request negotiation or request synchronization).
Would it be better to split this into two different messages (and adjust various
message names accordingly)?
RESOLVED: Yes. Done.48. Should the Appendix "Capability Analysis of Current Protocols" be deleted before
RFC publication?
RESOLVED: No (per WG meeting at IETF 96).49. Should say more about signaling between two autonomic networks/domains.
RESOLVED: Description of separate GRASP instance added.50. Is Rapid mode limited to on-link only? What happens if first discovery responder does
not support Rapid Mode? , )
RESOLVED: Not limited to on-link. First responder wins.51. Should flooded objectives have a time-to-live before they are deleted from
the flood cache? And should they be tagged in the cache with their source locator?
RESOLVED: TTL added to Flood (and Discovery Response) messages. Cached flooded
objectives must be tagged with their originating ASA locator, and multiple copies must be kept if necessary.52. Describe in detail what is allowed and disallowed in an insecure instance of GRASP.
RESOLVED: Done.53. Tune IANA Considerations to support early assignment request.54. Is there a highly unlikely race condition if two peers simultaneously choose the
same Session ID and send each other simultaneous M_REQ_NEG messages?
RESOLVED: Yes. Enhanced text on Session ID generation, and added precaution when
receiving a Request message.55. Could discovery be performed over TCP?
RESOLVED: Unicast discovery added as an option.56. Change Session-ID to 32 bits?
RESOLVED: Done.57. Add M_INVALID message?
RESOLVED: Done.58. Maximum message size?
RESOLVED by specifying default maximum message size (2048 bytes).59. Add F_NEG_DRY flag to specify a "dry run" objective?.
RESOLVED: Done.60. Change M_FLOOD syntax to associate a locator with each objective?
RESOLVED: Done.61. Is the SONN constrained instance really needed?
RESOLVED: Retained but only as an option.62. Is it helpful to tag descriptive text with message names (M_DISCOVER etc.)?
RESOLVED: Yes, done in various parts of the text.63. Should encryption be MUST instead of SHOULD in and ?
RESOLVED: Yes, MUST implement in both cases.64. Should more security text be moved from the main text into the Security Considerations?
RESOLVED: No, on AD advice.65. Do we need to formally restrict Unicode characters allowed in objective names?
RESOLVED: No, but need to point to guidance from PRECIS WG.66. Split requirements into separate document?
RESOLVED: No, on AD advice.67. Remove normative dependency on draft-greevenbosch-appsawg-cbor-cddl?
RESOLVED: No, on AD advice. In worst case, fix at AUTH48.draft-ietf-anima-grasp-15, 2017-07-07:
Updates following additional IESG comments:
Security (Eric Rescorla): missing brittleness of group security concept, attack via compromised member.
TSV (Mirja Kuehlewind): clarification on the use of UDP, TCP, mandate use of TCP (or other reliable transport).
Clarified that in ACP, UDP is not used at all.
Clarified that GRASP itself needs TCP listen port (was previously written as if this was optional).
draft-ietf-anima-grasp-14, 2017-07-02:
Updates following additional IESG comments:
Updated 2.5.1 and 2.5.2 based on IESG security feedback (specify dependency against security substrate).
Strengthened requirement for reliable transport protocol.
draft-ietf-anima-grasp-13, 2017-06-06:
Updates following additional IESG comments:
Removed all mention of TLS, including SONN, since it was under-specified.
Clarified other text about trust and security model.
Banned Rapid Mode when multicast is insecure.
Explained use of M_INVALID to support extensibility
Corrected details on discovery cache TTL and discovery timeout.
Improved description of multicast UDP w.r.t. RFC8085.
Clarified when transport connections are opened or closed.
Noted that IPPROTO values come from the Protocol Numbers registry
Protocol change: Added protocol and port numbers to URI locator.
Removed inaccurate text about routing protocols
Moved Requirements section to an Appendix.
Other editorial and technical clarifications.
draft-ietf-anima-grasp-12, 2017-05-19:
Updates following IESG comments:
Clarified that GRASP runs in a single addressing realm
Improved wording about FQDN resolution, clarified that URI usage is out of scope.
Clarified description of negotiation timeout.
Noted that 'dry run' semantics are ASA-dependent
Made the ACP a normative reference
Clarified that LL multicasts are limited to GRASP interfaces
Unicast UDP moved out of scope
Editorial clarifications
draft-ietf-anima-grasp-11, 2017-03-30:
Updates following IETF 98 discussion:
Encryption changed to a MUST implement.
Pointed to guidance on UTF-8 names.
draft-ietf-anima-grasp-10, 2017-03-10:
Updates following IETF Last call:
Protocol change: Specify that an objective with no initial value should have
its value field set to CBOR 'null'.
Protocol change: Specify behavior on receiving unrecognized message type.
Noted that UTF-8 names are matched byte-for-byte.
Added brief guidance for Expert Reviewer of new generic objectives.
Numerous editorial improvements and clarifications and minor text rearrangements,
none intended to change the meaning.
draft-ietf-anima-grasp-09, 2016-12-15:
Protocol change: Add F_NEG_DRY flag to specify a "dry run" objective.
Protocol change: Change M_FLOOD syntax to associate a locator with each objective.
Concentrated mentions of TLS in one section, with all details out of scope.
Clarified text around constrained instances of GRASP.
Strengthened text restricting LL addresses in locator options.
Clarified description of rapid mode processsing.
Specified that cached discovery results should not be returned on the same interface where they were learned.
Shortened text in "High Level Design Choices"
Dropped the word 'kernel' to avoid confusion with o/s kernel mode.
Editorial improvements and clarifications.
draft-ietf-anima-grasp-08, 2016-10-30:
Protocol change: Added M_INVALID message.
Protocol change: Increased Session ID space to 32 bits.
Enhanced rules to avoid Session ID clashes.
Corrected and completed description of timeouts for Request messages.
Improved wording about exponential backoff and DoS.
Clarified that discovery relaying is not done by limited security instances.
Corrected and expanded explanation of port used for Discovery Response.
Noted that Discovery message could be sent unicast in special cases.
Added paragraph on extensibility.
Specified default maximum message size.
Added Appendix for sample messages.
Added short protocol overview.
Editorial fixes, including minor re-ordering for readability.
draft-ietf-anima-grasp-07, 2016-09-13:
Protocol change: Added TTL field to Flood message (issue 51).
Protocol change: Added Locator option to Flood message (issue 51).
Protocol change: Added TTL field to Discovery Response message (corrollary to issue 51).
Clarified details of rapid mode (issues 43 and 50).
Description of inter-domain GRASP instance added (issue 49).
Description of limited security GRASP instances added (issue 52).
Strengthened advice to use TCP rather than UDP.
Updated IANA considerations and text about well-known port usage (issue 53).
Amended text about ASA authorization and roles to allow for overlapping ASAs.
Added text recommending that Flood should be repeated periodically.
Editorial fixes.
draft-ietf-anima-grasp-06, 2016-06-27:
Added text on discovery cache timeouts.
Noted that ASAs that are only initiators do not need to respond to discovery message.
Added text on unexpected address changes.
Added text on robust implementation.
Clarifications and editorial fixes for numerous review comments
Added open issues for some review comments.
draft-ietf-anima-grasp-05, 2016-05-13:
Noted in requirement T1 that it should be possible to implement ASAs independently as user space programs.
Protocol change: Added protocol number and port to discovery response. Updated protocol description, CDDL and IANA considerations accordingly.
Clarified that discovery and flood multicasts are handled by the GRASP core, not directly by ASAs.
Clarified that a node may discover an objective without supporting it for synchronization or negotiation.
Added Implementation Status section.
Added reference to SCSP.
Editorial fixes.
draft-ietf-anima-grasp-04, 2016-03-11:
Protocol change: Restored initiator field in certain messages and adjusted relaying rules
to provide complete loop detection.
Updated IANA Considerations.
draft-ietf-anima-grasp-03, 2016-02-24:
Protocol change: Removed initiator field from certain messages and adjusted relaying requirement
to simplify loop detection. Also clarified narrative explanation of discovery relaying.
Protocol change: Split Request message into two (Request Negotiation and Request Synchronization)
and updated other message names for clarity.
Protocol change: Dropped unused Device ID option.
Further clarified text on transport layer usage.
New text about multicast insecurity in Security Considerations.
Various other clarifications and editorial fixes, including moving some material to Appendix.
draft-ietf-anima-grasp-02, 2016-01-13:
Resolved numerous issues according to WG discussions.
Renumbered requirements, added D9.
Protocol change: only allow one objective in rapid mode.
Protocol change: added optional error string to DECLINE option.
Protocol change: removed statement that seemed to say that a Request not preceded
by a Discovery should cause a Discovery response. That made no sense, because there
is no way the initiator would know where to send the Request.
Protocol change: Removed PEN option from vendor objectives, changed naming rule
accordingly.
Protocol change: Added FLOOD message to simplify coding.
Protocol change: Added SYNCH message to simplify coding.
Protocol change: Added initiator id to DISCOVER, RESPONSE and FLOOD messages.
But also allowed the relay process for DISCOVER and FLOOD to regenerate a Session ID.
Protocol change: Require that discovered addresses must be global (except during bootstrap).
Protocol change: Receiver of REQUEST message must close socket if no ASA is listening for the objective.
Protocol change: Simplified Waiting message.
Protocol change: Added No Operation message.
Renamed URL locator type as URI locator type.
Updated CDDL definition.
Various other clarifications and editorial fixes.
draft-ietf-anima-grasp-01, 2015-10-09:
Updated requirements after list discussion.
Changed from TLV to CBOR format - many detailed changes, added co-author.
Tightened up loop count and timeouts for various cases.
Noted that GRASP does not provide transactional integrity.
Various other clarifications and editorial fixes.
draft-ietf-anima-grasp-00, 2015-08-14:
File name and protocol name changed following WG adoption.
Added URL locator type.
draft-carpenter-anima-gdn-protocol-04, 2015-06-21:
Tuned wording around hierarchical structure.
Changed "device" to "ASA" in many places.
Reformulated requirements to be clear that the ASA is the main customer
for signaling.
Added requirement for flooding unsolicited synch, and added it to protocol spec.
Recognized DNCP as alternative for flooding synch data.
Requirements clarified, expanded and rearranged following design team discussion.
Clarified that GDNP discovery must not
be a prerequisite for GDNP negotiation or synchronization (resolved issue 13).
Specified flag bits for objective options (resolved issue 15).
Clarified usage of ACP vs TLS/DTLS and TCP vs UDP (resolved issues 9,10,11).
Updated DNCP description from latest DNCP draft.
Editorial improvements.draft-carpenter-anima-gdn-protocol-03, 2015-04-20:
Removed intrinsic security, required external security
Format changes to allow DNCP co-existence
Recognized DNS-SD as alternative discovery method.
Editorial improvementsdraft-carpenter-anima-gdn-protocol-02, 2015-02-19:
Tuned requirements to clarify scope,
Clarified relationship between types of objective,
Clarified that objectives may be simple values or complex data structures,
Improved description of objective options,
Added loop-avoidance mechanisms (loop count and default timeout,
limitations on discovery relaying and on unsolicited responses),
Allow multiple discovery objectives in one response,
Provided for missing or multiple discovery responses,
Indicated how modes such as "dry run" should be supported,
Minor editorial and technical corrections and clarifications,
Reorganized future work list. draft-carpenter-anima-gdn-protocol-01, restructured the logical flow of the document,
updated to describe synchronization completely, add unsolicited responses, numerous corrections
and clarifications, expanded future work list, 2015-01-06. draft-carpenter-anima-gdn-protocol-00, combination
of draft-jiang-config-negotiation-ps-03 and
draft-jiang-config-negotiation-protocol-02, 2014-10-08.For readers unfamiliar with CBOR, this appendix shows a number of example GRASP
messages conforming to the CDDL syntax given
in . Each message is shown three times in the following formats:
CBOR diagnostic notation.Similar, but showing the names of the constants. (Details of the flag bit encoding are omitted.) Hexadecimal version of the CBOR wire format.
Long lines are split for display purposes only.The initiator (2001:db8:f000:baaa:28cc:dc4c:9703:6781) multicasts a discovery message
looking for objective EX1:A peer (2001:0db8:f000:baaa:f000:baaa:f000:baaa) responds with a locator:The initiator multicasts a flood message. The single objective has a null locator. There is no response:Following successful discovery of objective EX2, the initiator unicasts a request:The peer responds with a value:Following successful discovery of objective EX3, the initiator unicasts a request:The peer responds with immediate acceptance. Note that no objective is needed,
because the initiator's request was accepted without change:Again the initiator unicasts a request:The responder starts to negotiate (making an offer):The initiator continues to negotiate (reducing its request, and note that the loop count is decremented):The responder asks for more time:The responder continues to negotiate (increasing its offer):The initiator continues to negotiate (reducing its request):The responder refuses to negotiate further:This negotiation has failed. If either side had sent
[M_END, 13767778, [O_ACCEPT]] it would have succeeded, converging
on the objective value in the preceding M_NEGOTIATE. Note that apart
from the initial M_REQ_NEG, the process is symmetrical.This section discusses the requirements for discovery, negotiation
and synchronization capabilities. The primary user of the protocol is an autonomic service
agent (ASA), so the requirements are mainly expressed as the features needed by an ASA.
A single physical device might contain several ASAs, and a single ASA might manage
several technical objectives. If a technical objective is managed by several ASAs,
any necessary coordination is outside the scope of the GRASP signaling protocol.
Furthermore, requirements for ASAs themselves, such as the processing of Intent
, are out of scope for the present document.D1. ASAs may be designed to manage any type of configurable device or software,
as required in . A basic requirement
is therefore that the protocol can represent and discover any
kind of technical objective (as defined in )
among arbitrary subsets of participating nodes.In an autonomic network we must assume that when a device starts up
it has no information about any peer devices, the network structure,
or what specific role it must play. The ASA(s) inside the device are
in the same situation. In some cases, when a new application session
starts up within a device, the device or ASA may again lack
information about relevant peers. For example, it might be necessary to set
up resources on multiple other devices, coordinated and matched to
each other so that there is no wasted resource. Security settings
might also need updating to allow for the new device or user.
The relevant peers may be different for different technical
objectives. Therefore discovery needs to be repeated as often as
necessary to find peers capable of acting as counterparts for each
objective that a discovery initiator needs to handle.
From this background we derive the next three requirements:D2. When an ASA first starts up, it may have no knowledge of the specific network to
which it is attached.
Therefore the discovery process must be able to support any network scenario,
assuming only that the device concerned is bootstrapped from factory condition.
D3. When an ASA starts up, it must require no configured location information about any
peers in order to discover them.D4. If an ASA supports multiple technical objectives, relevant peers may be different
for different discovery objectives, so discovery needs to be performed separately to
find counterparts for each objective. Thus, there must be a mechanism by
which an ASA can separately discover peer ASAs for each of the
technical objectives that it needs to manage, whenever necessary.D5. Following discovery, an ASA will normally perform negotiation
or synchronization for the corresponding objectives. The design
should allow for this by conveniently linking discovery to negotiation
and synchronization. It may provide an optional mechanism to
combine discovery and negotiation/synchronization in a single protocol exchange.D6. Some objectives may only be significant on the local link,
but others may be significant across the routed network and require
off-link operations. Thus, the relevant peers might be immediate
neighbors on the same layer 2 link, or they might be more distant and
only accessible via layer 3. The mechanism must therefore provide both
on-link and off-link discovery of ASAs supporting specific technical
objectives.D7. The discovery process should be flexible enough to allow for
special cases, such as the following:
During initialization, a device must be able to establish mutual trust
with autonomic nodes elsewhere in the network and participate in an
authentication mechanism. Although
this will inevitably start with a discovery action, it is a special case
precisely because trust is not yet established. This topic
is the subject of .
We require that once trust has been established for a device,
all ASAs within the device inherit the device's credentials and are also trusted.
This does not preclude the device having multiple credentials.
Depending on the type of network involved, discovery of other
central functions might be needed, such as
the Network Operations Center (NOC) .
The protocol must be capable of supporting such discovery during initialization,
as well as discovery during ongoing operation.D8. The discovery process must not generate excessive traffic and
must take account of sleeping nodes. D9. There must be a mechanism for handling stale discovery results.Autonomic networks need to be able to manage many
different types of parameter and consider many dimensions,
such as latency, load, unused or limited resources,
conflicting resource requests,
security settings, power saving, load balancing, etc.
Status information and resource metrics need to be shared between
nodes for dynamic adjustment of resources and for monitoring purposes.
While this might be achieved by existing protocols when they are
available, the new protocol needs to be able to support parameter
exchange, including mutual synchronization, even when no negotiation
as such is required. In general, these parameters do not apply to all
participating nodes, but only to a subset. SN1. A basic requirement for the protocol is therefore the
ability to represent, discover, synchronize and negotiate almost any
kind of network parameter among selected subsets of participating nodes.SN2. Negotiation is an iterative request/response process that must be guaranteed to terminate
(with success or failure). While tie-breaking rules must be defined specifically
for each use case, the protocol should have some general mechanisms in support of loop
and deadlock prevention, such as hop count limits or timeouts.SN3. Synchronization must be possible for groups of nodes ranging from small to very large.
SN4. To avoid "reinventing the wheel", the protocol should be able to encapsulate the
data formats used by existing configuration protocols (such as NETCONF/YANG)
in cases where that is convenient.SN5. Human intervention in complex situations is costly and error-prone.
Therefore, synchronization or negotiation of parameters without human
intervention is desirable whenever the coordination of multiple devices can improve
overall network performance. It follows that the protocol's resource requirements
must be small enough to fit in any device that would otherwise need human intervention.
The issue of running in constrained nodes
is discussed in .SN6. Human intervention in large networks is often replaced by use of a
top-down network management system (NMS). It therefore follows that
the protocol, as part of the Autonomic Networking Infrastructure, should
be capable of running in any device that would otherwise be managed by
an NMS, and that it can co-exist with an NMS, and with protocols
such as SNMP and NETCONF.SN7. Specific autonomic features are expected to be implemented by individual ASAs,
but the protocol must be general enough to allow them. Some examples follow:
Dependencies and conflicts: In order to
decide upon a configuration for a given device, the device may need
information from neighbors. This can be established through the
negotiation procedure, or through synchronization if that
is sufficient. However, a given item in a neighbor
may depend on other information from its own neighbors, which may
need another negotiation or synchronization procedure to obtain or decide.
Therefore, there are potential dependencies and conflicts among negotiation or synchronization
procedures. Resolving dependencies and conflicts is a matter for the individual ASAs involved.
To allow this, there need to be clear boundaries and convergence
mechanisms for negotiations. Also some mechanisms are needed to avoid
loop dependencies or uncontrolled growth in a tree of dependencies.
It is the ASA designer's responsibility
to avoid or detect looping dependencies or excessive growth of dependency trees.
The protocol's role is limited to bilateral signaling between ASAs,
and the avoidance of loops during bilateral signaling.Recovery from faults and identification of faulty devices should be
as automatic as possible. The protocol's role is limited to discovery, synchronization and
negotiation. These processes can occur at any time, and an ASA may
need to repeat any of these steps when the ASA detects an event
such as a negotiation counterpart failing.Since a major goal is to minimize human intervention, it is necessary that the
network can in effect "think ahead" before changing its parameters. One aspect
of this is an ASA that relies on a knowledge base to predict network behavior.
This is out of scope for the signaling protocol. However, another aspect is
forecasting the effect of a change by a "dry run" negotiation before actually
installing the change. Signaling a dry run is therefore a desirable feature
of the protocol. Note that management logging, monitoring, alerts and tools for intervention are required.
However, these can only be features of individual ASAs, not of the protocol itself.
Another document discusses how
such agents may be linked into conventional OAM systems via an Autonomic Control Plane
. SN8. The protocol will be able to deal with a wide variety of
technical objectives, covering any type of network parameter.
Therefore the protocol will need a flexible and easily extensible format for
describing objectives. At a later stage it may be desirable to adopt an explicit
information model. One consideration is whether to adopt an existing
information model or to design a new one. T1. It should be convenient for ASA designers to define new technical objectives
and for programmers to express them, without excessive impact on
run-time efficiency and footprint. In particular, it should be convenient for ASAs
to be implemented independently of each other as user space programs rather than as kernel
code, where such a programming model is possible. The classes of device in which the protocol
might run is discussed in .
T2. The protocol should be easily extensible in case the initially defined discovery,
synchronization and negotiation mechanisms prove to be insufficient. T3. To be a generic platform, the protocol payload format should be
independent of the transport protocol or IP version.
In particular, it should be able to run over IPv6 or IPv4.
However, some functions, such as multicasting on
a link, might need to be IP version dependent. By default, IPv6 should
be preferred.T4. The protocol must be able to access off-link counterparts via routable addresses,
i.e., must not be restricted to link-local operation.T5. It must also be possible for an external discovery mechanism
to be used, if appropriate for a given technical objective. In other words, GRASP discovery
must not be a prerequisite for GRASP negotiation or synchronization. T6. The protocol must be capable of distinguishing multiple simultaneous
operations with one or more peers, especially when wait states occur.T7. Intent: Although the distribution of Intent is out of scope
for this document, the protocol must not by design exclude its
use for Intent distribution. T8. Management monitoring, alerts and intervention:
Devices should be able to report to a monitoring
system. Some events must be able to generate operator alerts and
some provision for emergency intervention must be possible (e.g.
to freeze synchronization or negotiation in a mis-behaving device). These features
might not use the signaling protocol itself, but its design should not exclude such use.T9. Because this protocol may directly cause changes to device configurations
and have significant impacts on a running network, all protocol exchanges need to be
fully secured against forged messages and man-in-the middle attacks, and secured
as much as reasonably possible against denial of service attacks. There must also
be an encryption mechanism to resist unwanted monitoring. However, it is not required
that the protocol itself provides these security features; it may depend on an existing
secure environment. This appendix discusses various existing protocols with properties
related to the requirements described in . The
purpose is to evaluate whether any existing protocol, or a simple
combination of existing protocols, can meet those requirements.Numerous protocols include some form of discovery, but these all appear to be very
specific in their applicability. Service Location Protocol (SLP)
provides service discovery for managed networks,
but requires configuration of its own servers. DNS-SD
combined with mDNS provides service discovery for
small networks with a single link layer.
aims to extend this to larger autonomous networks but this is not yet
standardized. However, both SLP and DNS-SD appear to
target primarily application layer services, not the layer 2 and 3 objectives
relevant to basic network configuration. Both SLP and DNS-SD are text-based protocols. Simple Network Management Protocol (SNMP) uses
a command/response model not well suited for peer negotiation. Network Configuration
Protocol (NETCONF) uses an RPC model that does allow positive or
negative responses from the target system, but this is still not
adequate for negotiation.There are various existing protocols that have elementary negotiation
abilities, such as Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
, Neighbor Discovery (ND) ,
Port Control Protocol (PCP) , Remote Authentication
Dial In User Service (RADIUS) , Diameter ,
etc. Most of them are configuration or
management protocols. However, they either provide only a simple
request/response model in a master/slave context or very limited
negotiation abilities.There are some signaling protocols with an element of negotiation.
For example Resource ReSerVation Protocol (RSVP)
was designed for negotiating quality of service
parameters along the path of a unicast or multicast flow. RSVP is a very
specialised protocol aimed at end-to-end flows.
A more generic design is General Internet
Signalling Transport (GIST) , but it is
complex, tries to solve many problems, and is also aimed at per-flow
signaling across many hops rather than at device-to-device signaling.
However, we cannot completely exclude extended RSVP or GIST as a
synchronization and negotiation protocol. They do not appear to be
directly useable for peer discovery.RESTCONF is a protocol intended to
convey NETCONF information expressed in the YANG language via HTTP,
including the ability to transit HTML intermediaries. While this is a
powerful approach in the context of centralised configuration of a
complex network, it is not well adapted to efficient interactive
negotiation between peer devices, especially simple ones that might
not include YANG processing already.The Distributed Node Consensus Protocol (DNCP)
is defined as a generic form
of state synchronization protocol, with a proposed usage profile being the
Home Networking Control Protocol (HNCP)
for configuring Homenet routers. A specific application of DNCP for autonomic
networking was proposed in .
DNCP "is designed to provide a way for each participating node to
publish a set of TLV (Type-Length-Value) tuples, and to provide a
shared and common view about the data published... DNCP is most suitable
for data that changes only infrequently... If constant rapid
state changes are needed, the preferable choice is to use an
additional point-to-point channel..."Specific features of DNCP include:
Every participating node has a unique node identifier.DNCP messages are encoded as a sequence of TLV objects, sent over
unicast UDP or TCP, with or without (D)TLS security.Multicast is used only for discovery of DNCP neighbors
when lower security is acceptable.Synchronization of state is maintained by a flooding process using the Trickle algorithm.
There is no bilateral synchronization or negotiation capability.The HNCP profile of DNCP is designed to operate between directly connected neighbors
on a shared link using UDP and link-local IPv6 addresses.
DNCP does not meet the needs of a general negotiation protocol, because it is designed
specifically for flooding synchronization. Also, in its HNCP profile it is limited to link-local
messages and to IPv6. However, at the minimum it is a
very interesting test case for this style of interaction between devices
without needing a central authority, and it is a proven method of network-wide state
synchronization by flooding.The Server Cache Synchronization Protocol (SCSP) also describes
a method for cache synchronization and cache replication among a group of nodes.A proposal was made some years ago for an IP based Generic Control Protocol
(IGCP) . This was aimed
at information exchange and negotiation but not directly at peer
discovery. However, it has many points in common with the present work.None of the above solutions appears to completely meet the needs of
generic discovery, state synchronization and negotiation in a single solution.
Many of the protocols assume that they are working in a traditional
top-down or north-south scenario, rather than a fluid peer-to-peer
scenario. Most of them are specialized in one way or another. As a result,
we have not identified a combination of existing protocols that meets the
requirements in . Also, we have not identified a path
by which one of the existing protocols could be extended to meet the
requirements.